BuildPhysics
Complete feature reference
Search the exact name of a button, object, setting, measurement, or physics rule. This guide explains where to find it, how to use it, and the model details that can change the result.
· Applies to the current BuildPhysics website
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The welcome screen offers four starting paths: Experiment, Interactive Lessons, Tutorials, and Power Core: Physics Trials. Experiment opens the sandbox; the other choices open their corresponding menus.
Where: It opens for a new visitor. Reopen it at any time with the house-shaped Home button in the top toolbar or workspace rail. Closing Home does not clear the current world.
The left workspace rail opens the four primary panels. Create contains building tools and shared world settings. Properties shows live measurements and editable settings for the selected item. Guide shows the investigation question and suggested trial steps for the loaded experiment. Data contains graphs, recent samples, and system totals.
Close a panel with its × button. On smaller screens, opening one large panel closes the others so the simulation remains usable.
Choose Select / move, then click an item in the world or choose it from the Objects list. While the trial is paused, drag an object to move it and use the visible handles to resize, rotate, curve, or reconnect it when that item supports those actions.
Shortcut: S or Esc. Properties that change the starting setup are locked while the simulation is running.
Pan / zoom moves the camera without moving objects. Use the mouse wheel or trackpad to zoom. The − and + buttons in the world change zoom, and Fit view or Fit entire experiment frames the full setup.
If camera following is enabled for an object, manually dragging the stage temporarily suspends following. Resetting or using the object’s follow control resumes it according to the control’s description.
Prepared experiments can hide controls that belong to later AP Physics 1 units. With Unit Limited Settings on, the interface shows concepts introduced through the loaded experiment’s unit. Turn it off to temporarily expose all tools, properties, measurements, and displays.
Custom worlds expose all features automatically. If a button or graph variable appears to be missing, check this setting before assuming the feature is unavailable.
The Objects section in Properties lists selectable items in the current scene. Choosing one selects the same item in the world. This is useful when objects overlap or a small connection is difficult to click. Choose Multi-select in Build to show selection checkboxes, or Shift-click to select several objects.
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Choose a prepared experiment or custom starting world from Experiment, then press Load. Loading replaces the current setup, so save work you want to keep first.
Ground only starts with an infinite ground surface, the Outdoor Ground background, and Grid & axes on. It is also the default workspace opened by Experiment on the home screen. Blank world removes even the ground. Unit blank worlds start empty while organizing controls around that AP Physics 1 unit.
The document icon beside Experiment opens downloadable PDF and editable Word resources for the selected prepared lab. A custom or blank world may not have an associated document.
Run advances simulated time and changes to Pause while active. Pause freezes the model at its current state without discarding collected data. Press Space to toggle Run and Pause when focus is not inside an editable field.
Starting-state properties are disabled during Run to prevent a trial from changing underneath the solver. Pause before moving objects or editing inputs.
Open the stopwatch next to Run to enter an automatic stopping time in simulated seconds. Leave the field blank or choose Run indefinitely for no limit. The simulation pauses at the requested boundary so the final data sample ends cleanly at that time.
Step advances exactly one 1/240-second physics step while paused. Use it to inspect the beginning of a collision or see how forces change one solver step at a time. Shortcut: ..
Reset returns the trial to the starting conditions captured when Run began. It keeps model settings and object arrangement, but clears the current trial’s clock and sampled data. Shortcut: R.
Clear trial data erases graphs and table samples without changing the setup or current object state. Clear world removes the scene so you can build from scratch. Loading an experiment reconstructs that experiment’s original prepared setup.
The Speed menu changes how quickly simulated time is displayed, from 0.1× to 4×. It does not change the physical equations or the 1/240-second solver step. Use slower playback for fast events and faster playback for long-period motion.
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Choose Draw surface, then click two endpoints or press and drag. Select the surface afterward to edit its endpoints, make it curved, extend it forever, or give it prescribed velocity and acceleration.
Objects placed close to a surface can snap into contact while paused. Curved surfaces include a middle curve handle.
Choose Add block and drag a rectangle in the world. Blocks support mass, width, height, contact properties, applied forces, translation, and optional torque-driven rotation.
Choose Add disk to place the round object shown on the main button, or use its arrow to switch between Disk, Hoop, Bowling Ball, and Soccer Ball. Choosing an option activates placement immediately; drag from the center outward to set its radius. Each preset starts with the appropriate Inertia factor in I = factor · mR²: 0.50 for a solid cylinder, 1.00 for a thin ring, 0.40 for a solid sphere, and 0.67 for a hollow sphere. You can still edit that factor in Properties.
Click a center and edge, or drag outward, to create a fixed pulley. Route a rope through it by clicking the first endpoint, each pulley in order, and the final endpoint. Properties can switch between a massless pulley and one with mass and moment of inertia.
Draw a long rectangle. A new beam begins with a fixed pivot at its center. Select it to move the triangular pivot marker, rotate it with the round handle, apply off-center forces, or turn the fixed pivot off so the beam translates, rotates, and collides freely.
Choose Cannon under Interactives, then click to place it. Select the cannon to see its Aim and Fire controls. Press Run, set an aim angle, and click Fire. Positive angles turn counterclockwise from the cannon’s local right direction. Multiple cannons can share a scene; the controls operate the selected one.
Use the live −180° to 180° slider to change aim and the adjacent control to change launch speed before or during a run. While paused, you can also drag the round rotation handle beyond the selected cannon’s muzzle or type an exact angle in Quick properties. Quick properties also includes the Anchored (no recoil) option. New cannons start aimed at 0°. Open Settings to set cannon mass, projectile mass, radius, and starting launch speed. The Appearance & display section lets you rename or recolor the cannon, turn its vectors on, and follow it with the camera. Cannon vectors start off. Cannons start anchored. Uncheck Anchored (no recoil) to let the cannon move and recoil. Launch speed is measured relative to the cannon after firing. The barrel pivots through the center of mass, and the cannon does not rotate. Only the base collides; the barrel is a visual aiming guide.
Each click loads and fires a new projectile; cannon mass stays constant. A free cannon and its newly loaded projectile share the cannon’s velocity before the firing impulse. Projectiles behave like ordinary disks, with gravity, collisions, and graph data. A blocked muzzle prevents firing. Shots have a 0.2-second simulated reload interval and count toward the scene’s 100-body limit. Reset removes projectiles fired during the current run and restores the starting aim. Saved scenes preserve cannon settings and any projectiles already present.
Choose Rocket under Interactives and click to place it. Press Run, then hold ↑ for forward thrust, ↓ for reverse thrust, ← for counterclockwise steering torque, or → for clockwise steering torque. The on-stage controls provide the same four inputs.
The Rocket is force driven: releasing the keys stops the engine or steering torque but does not erase momentum. Gravity, drag, collisions, mass, and rotational inertia determine the resulting motion. It starts pointing upward with vectors hidden and camera follow on. Only one Pusher, Puller, or Rocket can be present because they share the live arrow controls.
Choose Conveyor under Interactives, then click or drag from one endpoint to the other. The belt has a fixed thickness and starts stopped. Press Run, then use the live controls to run it forward, reverse it, stop it, or change its speed. Forward follows the conveyor’s local right direction.
You can place multiple conveyors. The control menu targets the selected conveyor, a named conveyor, or all conveyors at once. While paused, drag either endpoint to change both length and angle. Quick properties provides the starting direction, angle in degrees, and custom friction settings; length and position remain available in Properties. New conveyors have custom friction enabled so they can move objects. If the master Friction control is off, the live controls explain that the belt cannot transfer motion and provide a Turn friction on button.
Place the Puller drone, press Run, and use all four arrow keys to fly. Press G to grab the nearest movable object within Grab range; press G again to release it. The released object keeps the Puller’s current velocity.
Important: diagonal input is normalized, so it does not exceed the configured Maximum flight speed. A Puller and its payload share that strict speed limit. Maximum rotor thrust must cover hovering, payload weight, acceleration, and braking. Release the arrows to brake and hover. Only one controlled actor can be added to a scene.
Place the Pusher and press Run. With gravity on, use ← and → to move and ↑ to jump while supported. With gravity off, all four arrow keys fly. Arrow controls pause while a form field is being edited.
With friction, movement uses walking traction. Without friction, the visible jetpack supplies surface motion and airborne steering. Holding an arrow into an object maintains the configured constant Push force, even if following that object temporarily exceeds Movement speed. Releasing the arrow stops the push immediately, brakes back to the speed limit in about 0.15 s, then toward rest in about 0.5 s. Only one controlled actor can be added.
A planet is a circular body that attracts other objects using Newtonian gravity, F = Gm₁m₂/r². Its mass can be very large. Turning off ordinary World gravity does not disable a planet’s gravitational attraction.
Click an edge point on one object or surface, then an edge point on another. The joint keeps those points together while allowing the connected objects to rotate. This differs from a completely inelastic stuck contact, which also locks relative rotation.
Click a body or surface endpoint, optionally click one or more pulleys in route order, then click the final endpoint. The rope is massless and inextensible and enforces a maximum path length. Detailed attachment behavior is covered under Rope attachments.
Start on a body for a traditional connection. Start on a surface to mount a reusable spring that can later attach to a mass. Drag endpoints to reconnect or detach them, and drag the x = 0 marker to change the relaxed endpoint position.
Place a compression launcher with a base and platform. It pushes objects outward when they touch it inside its relaxed length. Properties control spring constant, relaxed length, platform width, and base position.
Start the arrow on a body and drag outward. Applied-force display turns on automatically so the new vector is visible. Edit magnitude, angle, or x/y components in Properties; synchronized fields update together. When rotation is unlocked on a supported shape, the application point can create torque. Beams can keep a force fixed to the screen or rotating with the beam.
Click a body and drag the velocity arrow to set its starting velocity. Velocity-vector display turns on automatically. Select the arrow to resize or re-angle it. Deleting the selected velocity arrow sets that body’s velocity to zero.
Click a body and drag to request an initial acceleration vector. Acceleration-vector display turns on automatically. BuildPhysics adds only the applied-force correction needed beyond the object’s current force balance. A request parallel to a supporting surface leaves its balancing weight and normal force intact. A request away from the surface is treated as lift-off: the force includes enough to overcome gravity and the separating contact force drops to zero, so the initial acceleration follows the drawn direction. Later contacts and other forces can still change the net acceleration during the run.
Click a body and drag an impulse arrow. The preview shows both impulse in N·s and the resulting Δv. Before running, switch to Select and drag anywhere on the impulse arrow to change its magnitude and direction, or edit it precisely in Properties. The impulse remains visible until you press Run or Step, when it is applied once; Reset restores it for another trial. Its natural unit is N·s, equivalent to kg·m/s.
For a force applied over time, click the impulse arrow and choose Advanced in its Quick properties menu. Select Force over time, then choose a constant force or a triangular force that rises from zero to a peak and falls back to zero. Set the force in newtons and duration in seconds; the graph previews the shape and total impulse. The arrow sets the direction and application point. The force starts on Run or Step, continues across pauses, and repeats after Reset. Total impulse is force × duration for a constant force and half peak force × duration for a triangular force.
Set magnitude, direction, and application point in Properties. On an unlocked disk, hoop, block, or beam, an off-center impulse changes both linear and angular velocity.
For displacement, click or drag between two points. Properties show Δr, and the x/y components appear when component display is enabled. For angle, click the vertex, then a point on the starting ray to set 0°, then a point on the ending ray. The smaller angle between the rays (0°–180°) is shown. The dashed ray marks the starting direction. In Select mode, drag the vertex or either ray endpoint, or drag a ray to move the whole measurement. Handles snap near a surface; Properties also lets you enter all three points. Press Escape to cancel an unfinished measurement.
Drag between two points to place the sensor pods. The photogate does not collide with objects. Each object that crosses the beam adds its name, simulation time, and signed velocity to the selected photogate’s Quick properties table. The sign follows the arrow shown beside the beam. Use Reverse + direction to flip that convention and Clear data to start a fresh set of readings. Drag either pod to change the gate’s length or angle, or drag the beam to move the whole gate.
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Live measurements are calculated from the current simulation state. Editable properties define the setup or object model. Pause before editing. Initial position and motion controls are grouped under Appearance & display, since most users position objects and draw vectors directly in the simulation. Position, velocity, acceleration, energy, momentum, torque, and angular quantities update according to the selected object type and enabled curriculum unit.
Click an applied-force arrow and choose Advanced in its Quick properties menu. Choose Formula to enter a force magnitude in newtons, such as 5+2*t or -4*x, or choose Piecewise to build a force from linear segments. Both modes can depend on Time, t, Object x position, or Object y position. Positive force values follow the arrow's positive direction; negative values reverse it. Dragging a variable-force arrow changes its direction; choose Constant to return to a fixed magnitude. Rules are retained when saving scenes and resetting trials.
In Piecewise mode, give each segment a starting and ending force. For time, enter its duration: for example, 0 to 5 N over 5 s, followed by 6 to 2 N over the next 3 s. For position, enter the segment's starting and ending coordinate in metres. Use Add segment to extend the profile, and choose whether to hold the final force or return to zero at the end. The preview shows the ramps and jumps. Position profiles use the object's current center of mass, so moving backward retraces the same force relationship.
For either x-position or y-position rules, Advanced also shows the object's current x and y position. Edit either coordinate directly in those boxes; both remain available whichever position variable you choose. The force preview uses the drafted coordinates. Apply saves the position and force together; Cancel leaves the object unchanged. Position values use world metres.
Selecting a body, surface, force, velocity arrow, or connection can open a floating Quick properties card over the stage. Edit the common fields there, or choose All Properties to open the complete inspector. The card hides while the full Properties panel is open or when it has been closed for the current selection.
In both mechanics and fluids, open Appearance & display and clear Display name to hide the selected object's or surface's name on the canvas. It starts checked. This keeps the item and its measurement readings visible, and the choice is saved with the scene. Names remain available in Properties and object lists.
Make a copy duplicates the selected object or assembly with a small offset. When both ends of a connection and its routed pulleys are included, the copy receives its own connection to the copied parts. Connections to objects outside the selection stay with the original. Delete removes the selected objects and any connections that depend on them. The floating × in the world performs the same deletion.
The Select multiple objects tool enables Multi-select for grouping, copying, and moving several parts.
Pause the trial, then Shift-click objects to add or remove them from the selection. Choose Multi-select to do the same without a keyboard, or drag a box over the parts you want. Assembly controls and checkboxes in Properties → Objects appear while multi-select is active or several parts are selected. A multiple selection shows Copy selection and Delete selection directly in Properties instead of individual object properties. When Properties is closed, its Quick properties menu provides Select connected, Group selection, Ungroup, and Edit members. Choose Edit members to inspect a single part of a named assembly. Select connected adds parts joined by ropes, springs, joints, or track links; ordinary contact with the floor does not group objects.
Drag a selected part to move the selection together. With the stage focused, the arrow keys nudge it and Shift with an arrow makes a larger move. Internal rope lengths, spring rest lengths, and attachment points stay intact. The assembly status identifies connections reaching outside the selection. Include the connected parts with Select connected, or choose Detach outside connections, before moving. Esc clears the selection or cancels a drag, and Undo restores a completed move in one step.
Open Properties → Assemblies → Group parts, enter a name, and choose Group selection. Selecting a grouped part selects the assembly. Choose Edit members to work with its individual parts, then group the revised selection. Ungroup keeps all the parts and removes the group. The Groups list above Objects always shows your named groups, so you can select them without entering multi-select first. Groups with fewer than two parts are removed automatically. Named groups are preserved in saved scenes and Undo history; each part keeps its own physics when you run.
Make a copy duplicates included parts and their internal connections with fresh IDs. If a connection reaches outside the selection, include its other endpoint and any routed pulleys to copy the full mechanism. The assembly status explains outside attachments. Controlled characters still follow the scene's existing one-character limit.
Rename objects to make the Objects list, graph title, and data export easier to understand. Show vectors for this object can suppress vectors on one body without changing the global display switches. Follow this object with camera automatically pans during Run; Pusher and Puller use specialized follow behavior.
In the regular sandbox, following uses smooth direction-aware composition and Cap at frame behavior by default. The camera keeps its current zoom while long vector arrows and their labels remain inside the visible simulation area. Manually panning suspends follow until it is resumed from the object control or by Reset.
Mass affects translation and rotation. x/y position and velocity define the starting state. Acceleration fields are calculated readouts after the model combines forces. Blocks use width and height; circular objects use radius and an inertia factor in I = factor · mR². Angular velocity follows the sign convention: positive is counterclockwise, negative is clockwise.
Fixed in place (center does not move) prevents translation of the center, but an unlocked disk can still rotate about that fixed center. Lock torque-driven rotation prevents spin caused by torque while still allowing translation unless Fixed in place is also selected.
Force treatment changes: with rotation unlocked, displayed force vectors appear at their physical application points and can create torque. With rotation locked, force vectors are displayed through the center of mass and torque-driven spin is suppressed. A locked block can still visually align with the surface or beam supporting it; that alignment is not free torque-driven rotation.
Each applied force has magnitude, angle, and component fields that remain synchronized. Rotation-capable bodies also expose local x/y application positions. Moving a force away from the center can create torque.
For a beam, Rotates with beam preserves the force direction relative to the beam as it turns. Fixed to screen preserves its world direction. The same numerical angle therefore describes different behavior under rotation.
The named collision behavior choices set restitution to 1 (Elastic), 0.5 (Partially elastic), or 0 (Completely inelastic). Custom allows any value from 0 to 1. Default collisions supplies the world default for contacts. Turn on Custom restitution for this surface or Custom restitution for this conveyor to reveal its local restitution control. A specific contact-pair setting takes priority over the local and world defaults.
If the effective restitution is 0, a stuck-contact joint can be created automatically at impact. That joint locks the contact points and relative rotation until deleted. Older scenes saved with the former lower restitution value rule are migrated to pair overrides when loaded so their previous collision behavior is preserved.
The master Friction control determines whether friction forces act. By default, the general μs and μk values apply to all contacts. Open Advanced friction settings and set Apply friction to to Custom settings only when friction should act only at configured surfaces, conveyors, and contacts.
Static friction adjusts to the amount required to prevent slipping, up to its maximum. Once sliding occurs, kinetic friction acts opposite relative sliding motion using the effective kinetic coefficient. Entering μs or μk does not mean the friction force is always μFN; that equality is the maximum for static friction and the model value for sliding kinetic friction.
Older scenes saved with the former lower of the two contacting coefficient values rule are migrated to explicit custom contact settings when loaded so their previous behavior is preserved.
Extend forever treats the straight surface as infinite. Turn it off to use finite endpoints and optionally enable Curved surface. Endpoint and curve-point fields provide numerical control.
Surface velocity and acceleration are prescribed inputs: they move the surface according to the values entered rather than solving its motion from a mass and net force. This supports elevators and moving tracks. Use Add elevator platform for a platform with prescribed vertical motion. In the surface’s collision settings, enable Custom friction or Custom restitution when needed. Custom settings for one exact contact still take priority.
Select a body or surface and open Properties → Contact settings to customize one interaction. Choose Add contact settings, select the other item under Interaction with…, then enable Custom restitution for this contact, Custom friction for this contact, or both. These pair settings apply only to that exact contact and take priority over surface and World defaults.
Use the × button on a pair card, titled Remove pair and use defaults, to return that interaction to the normal hierarchy. Custom contact settings are saved with the scene. A surface or conveyor uses the default friction until Custom friction for this surface or Custom friction for this conveyor is checked, and uses World restitution until its matching Custom restitution option is checked.
With Fixed pivot on, the pivot position is fixed in world space and the beam rotates about it. Pivot offsets locate the pivot along and across the beam. Angle can use radians or degrees. Angular damping removes rotational motion over time.
With Fixed pivot off, the beam is a free rigid body: it translates, rotates, and collides with surfaces. Moving the pivot changes both gravitational torque and the moment of inertia about the pivot.
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A rope is massless and inextensible. Center of mass (ideal motion) applies the constraint and tension through the object’s center while the visible rope stops at its boundary. This avoids adding torque and keeps the ideal translational relationship simple.
Fixed point on object attaches to a specific local point, so tension can create torque as the object rotates. With rotation locked, a fixed edge attachment can make the center-to-attachment radius change relative to the path, so use center-of-mass attachment when the intended model is an ideal point mass.
With Pulley has mass and moment of inertia off, the pulley is ideal and a routed rope has equal tension on both sides. With it on, the tension difference supplies the torque needed for angular acceleration. Mass, radius, and Inertia coefficient determine I; a solid disk uses 0.5.
Spring constant sets stiffness, Relaxed length defines x = 0, and Damping resists relative spring motion. A surface-mounted spring can choose an Attached mass from Properties.
Drag either endpoint onto a body or surface to reconnect. Pull an attached endpoint away or select it and choose Disconnect to detach. Drag the x = 0 marker to reposition the relaxed endpoint. Spring force follows extension or compression from the relaxed length.
The launcher is one-sided: it pushes an object outward while compressed and does not pull it back after separation. Live measurements include current length, compression, spring force, stored energy, and the object being pushed.
A user-created pin joint keeps two chosen edge points together while allowing relative rotation. A stuck contact created by a zero-restitution collision locks both the contact points and relative rotation. Select and delete either connection to separate the parts.
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Mass excludes the payload. Maximum flight speed is the strict combined speed limit while carrying. Maximum rotor thrust is shared across hovering, lifting, accelerating, and braking. Grab range measures the maximum edge-to-hook distance to the nearest movable object.
Push force is the constant normal force maintained while an arrow is held into an object. Movement speed is the walking or jetpack limit outside active contact-following. Jump impulse is applied only while supported with gravity on. Pusher friction limits walking traction; when friction is unavailable, the jetpack supplies motion instead.
Forward thrust and Reverse thrust set the engine forces applied along the Rocket’s local axis. Steering torque sets the rotational effect of the left and right controls. Quick properties exposes all three controls plus mass and camera follow; full Properties also includes name, color, vectors, starting position, heading, and angular velocity.
A planet is both a collidable circular body and a central gravity source. Increasing its mass increases its inverse-square attraction. Its force remains active even when the uniform World gravity switch is off.
Enable System center of mass to display the mass-weighted position. Selecting the marker shows total included mass, position, velocity, and acceleration, plus switches for center-of-mass velocity and acceleration vectors.
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The Gravity Enabled switch controls the uniform world field. Horizontal gx and vertical gy set its components; the usual Earth-like field is (0, −9.8) m/s². Turning the switch off removes this uniform field but does not turn off gravity produced by planet objects.
Linear drag adds a velocity-dependent resisting force with coefficient b in N·s/m. A value of zero is the ideal no-air-resistance model. Drag is separate from contact friction.
Turn Friction on to activate the saved setup or off to suppress every friction force without deleting coefficients or custom settings. With friction on, All contacts applies the general static and kinetic coefficients except where custom settings replace them. Custom settings only leaves other contacts frictionless.
Use the small arrow beside Add Block to choose Block, Cart, Car, Crate, Puck, or Sled. If an ordinary block is selected, choosing a style updates that object; otherwise it sets the style for the next block. Cart, Car, and Sled face the direction they are moving, including after a direction change.
The background-style split control offers None, Grid, Minimal Track, Road, Lab Floor, Outdoor Ground, and Sky. Grid draws grid lines without coordinate axes. Sky contains only sky and clouds. Road and Outdoor Ground include restrained world-fixed clouds, trees, and bushes, with clouds continuing vertically for free-fall scenes.
Grid & axes is an independent overlay. Turn it on to draw the grid and axes over any selected background style, or turn it off to see only the selected background.
Both selectors are visual only. Object mass, collision bounds, dimensions, friction, forces, and vector anchor points remain unchanged; a Road or Lab Floor never changes the surface model.
Grid & axes shows the +x-right, +y-up coordinate system. Motion trail records recent positions visually. Ticker Tape Motion shows faded position snapshots at the selected simulated Interval; Ticks shown limits how many snapshots remain visible. Its Interval and Ticks shown controls appear only after Ticker Tape Motion is checked. Velocity and acceleration switches show translational vectors. Angular velocity and angular acceleration use curved arrows; positive is counterclockwise and negative is clockwise.
Momentum, p shows each moving object's linear momentum, p = mv, from its center of mass in kg·m/s. It has its own switch, so momentum can be shown with or without velocity. Momentum arrows share the same scale: doubling mass at the same velocity doubles the arrow length. The vector detail controls also apply to momentum.
Total momentum, P shows the vector sum of the objects' momenta at the system center of mass, using the same momentum sum as the System tab. It includes the center-of-mass marker and can be shown independently of individual momentum arrows. Opposite momenta cancel; when the sum is zero, the display shows P = 0. The System center of mass switch can also keep the marker visible when total momentum is off.
These controls change visualization only. They do not add forces or alter motion.
Snap vectors while editing snaps an arrow within 3° of horizontal, vertical, or directions parallel/perpendicular to the supporting surface while placing or editing force, velocity, acceleration, and impulse arrows. Disable it for unrestricted angles.
Show switches between Vectors, Components, and Both. Component axes chooses x / y or ∥ / ⟂ to velocity. Values & units adds signed values. When a component coincides with its full vector, Both uses one arrow and a combined label; for a downward weight, W = −Wᵧ preserves the negative y-component. Angles measures direction from +x. Displacement measurements always use x / y axes.
Choose Components or Both under Show, then ∥ / ⟂ to velocity under Component axes. Each object's forces, velocity, acceleration, and momentum use that object's velocity direction. On a curved ramp, parallel acceleration changes speed and perpendicular acceleration changes direction. The positive perpendicular axis is 90° counterclockwise from velocity. At rest, the supporting surface tangent supplies the parallel direction; without a supporting surface, the display falls back to x / y. The axis choice also applies to graph component choices.
Show available forces enables the available force categories. Turn it off to isolate Weight, Normal, Applied, Spring, Tension, Joint/Pivot, or Friction. Net, ΣF adds the resultant external-force vector. Selected object only removes visual clutter. Force vector size scales every force arrow together without changing any force value or motion.
Hiding a force arrow never removes that force from the physics model.
Ground/contact (AP Physics 1) uses the point-mass classroom convention in which an object resting on the reference surface has Ug = 0. Center of mass (exact) measures height using the center.
Enable a custom Ug = 0 line to enter a reference height or set it from the selected object. Changing the reference changes potential-energy values, not forces or motion.
Hide closes individual workspace bars. Focus expands the working area. Projector mode, color theme, and text size adjust presentation. Graphics quality can remain Automatic or favor High quality or Performance. Display choices do not change the physical calculation.
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Open More → Creator Mode or press C. Choose a 16:9 or 9:16 recording frame, or No guide. Show guide changes only the overlay. Select an object or measurement and choose Frame Selection to fit its body, visible vectors, values, units, and labels inside the chosen frame.
Creator Mode hides the camera-follow eye. Object names are off by default and can be restored with Show object names. Play, Step, Reset, playback speed, and the visible timer use the same simulation state as the regular controls.
The Presentation menu controls Show vectors, Line thickness, Arrowhead size, Vector label size, Object label size, and Vector scale. Creator defaults use 250% line thickness, arrowheads, and vector labels; Vector scale starts at 100% and can be reduced to 10%. These values do not change the regular simulator’s vector styling.
Vector labels can show Variable + value, Value + unit, or Variable only. Show component subscripts controls the x/y subscripts, and Hide grid numbers starts on. Anchor vector labels to block keeps velocity and acceleration labels beside the vector origin as the block moves instead of allowing long vectors to carry labels toward the arrowhead.
Cap at frame preserves the camera zoom and caps an overlong arrow at the frame edge. Auto-scale vectors smoothly reduces the displayed vector scale as needed while keeping the physics value unchanged. Zoom to fit preserves full drawn vector length by smoothly widening the camera view.
With camera follow enabled, the followed object, arrowheads, and labels stay within the selected recording frame. Starting playback and changing direction use eased composition to avoid a sudden camera jump.
Show track tick marks adds subtle coordinate-fixed ticks without numbers. Show motion grid adds faint world-fixed vertical lines. Ticker Tape Motion (the older “Show motion trail” wording) leaves equally timed ghost positions that fade with age; its Interval and Ticks shown controls set the spacing and count. Because all three aids remain fixed in world coordinates, they scroll past a camera-followed object and reveal changes in speed.
Scene States capture named setups and Creator presentation choices for recall, update, copy, rename, or deletion. The first five can be recalled with 1–5. Each state also saves its camera-follow choice: recalling it follows the object that state saved, or follows nothing when the state was saved with camera follow off. A Data window already placed over the simulation remains available when entering Creator Mode.
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Measurements are sampled from simulated time at 30 Hz for scene bodies. The graph, recent-samples table, and CSV export use the same Object 1 and Object 2 choices in Graph. Object 1 follows the selected body unless you choose a named object; a named object stays the data source when you select something else on the canvas. Changing display settings does not erase collected data; Reset begins a new trial and clears its log.
Use the Y-axis controls first to enable up to three measurements. The first enabled series is the solid primary line used by Slope and Area. The X-axis can be Time or x position; units for slope and area change accordingly.
Available variables depend on the selected object, component mode, and Unit Limited Settings. In Fluids, Graph and Data measurement menus follow the chosen graph objects. A named Object 1 stays the source when you select something else on the canvas; two graph objects offer the combined set of relevant measurements. Specialized flow, parcel, and body measurements are grouped under Advanced. Diagnostic error values and volume-accounting details remain outside these menus.
In Data → Graph, use the controls over the graph’s bottom-right corner: − and + zoom, or hold Ctrl (Windows) or ⌘ (Mac) while scrolling over a plot to zoom around the pointer. Choose Pan to drag the graph; in Pan mode, scrolling or a two-finger pinch also zooms. Normal scrolling outside Pan mode still scrolls the Data panel. A middle-button drag pans without switching tools.
The toolbar identifies the active graph and shows Auto or Manual. Each graph in a two- or three-graph layout has its own view. Click a plot, navigate directly over it, or choose its measurement below the graph to target it. Choose Fit to restore automatic scaling for that plot and follow incoming data again. Manual views remain fixed while new samples arrive; changing the data source, axes, measurements, or trial resets the view.
For keyboard control, focus the graph with Tab: use + or − to zoom, the arrow keys to pan, and 0 or Home to fit. Hold Shift while using a zoom wheel gesture to change only the horizontal scale, or Alt to change only the vertical scale. Choose Inspect, Slope, or Area to leave Pan mode. Navigation changes the view while retaining the recorded values, selected analysis interval, and exported data.
Inspect reads the horizontal-axis value and enabled measurements at one sampled point. Click the graph to select the nearest exact recorded sample.
Slope estimates a local tangent using nearby samples. On x versus time, the slope is vx; on velocity versus time, it is acceleration. Area accepts two clicks or a drag interval and computes the signed trapezoidal area under the primary solid series. For velocity versus time, signed area is displacement; for force versus time, it is impulse.
The Data tab lists recent sampled values using the current measurement choices and graph objects. The heading names the data sources; when two objects are chosen, an Object column identifies each sample. Use it when exact numbers are more useful than a graph. For the full recorded dataset, choose Export CSV.
Open Two-dimensional collisions in Unit 4 of the Experiment library. In Simple mode, Mass A starts on the left moving right and Mass B starts at rest. Change the vertical offset to compare a central collision, an oblique collision, and a miss. In Advanced mode, set either mass's initial motion in any direction.
In Lab settings, choose velocity or momentum vectors. Turn Components on for x and y sliders, or off for magnitude and direction-angle sliders. Angles are measured counterclockwise from +x. Momentum controls use kg·m/s and set velocity through v = p/m; changing a mass keeps its velocity and updates its momentum. Simple mode holds the perpendicular motion and Mass B's motion at zero.
Choose Bounce (elastic) or Stick together under Collision behavior. Gravity, drag, and friction are off. For the student lab, keep Show x / y components on and compare total momentum before and after separately in each direction. With momentum vectors, add the two objects' signed components. With velocity vectors, first calculate each momentum component using p = mv. The handout uses four short trials covering both collision behaviors in Simple and Advanced modes, with no graphing.
Initial settings lock during a trial. Press Reset before changing them; Reset also separates objects that stuck together. Display controls remain available during a trial. Download the student handout through Lab resources.
The System tab summarizes energy and momentum for the current model. Bars show kinetic energy K, gravitational potential energy Ug, and spring potential energy Us; the scale adjusts to the current values. Numerical totals can include mechanical energy, linear momentum, and angular quantities when those concepts are available.
Potential-energy totals follow the selected Ug reference convention.
Clear trial data removes samples without changing the setup. Export CSV downloads all recorded measurements for the objects chosen in Graph. A two-object export includes object IDs and names, with each object's original sample times kept separately. Run a trial before exporting.
Choose Window to detach Graph, Data, and System into a movable, resizable window that can sit over the simulation—for example, beside a moving object. Drag its handle to place it and resize from the window edges or corner. The compact window layout keeps the graph controls and Inspect, Slope, or Area feedback close to the plot. Choose Dock to return it to the bottom.
In docked mode, drag the Data panel’s top separator or use keyboard controls when it is focused to change height. Maximize expands the full Data panel. Full screen expands only the graph; press Esc to exit. Window position and size persist for the session, including while Creator Mode is active.
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Undo and Redo in More restore recent setup edits. Ctrl+Z performs Undo. The history focuses on modeling changes rather than every camera or display action.
This downloads a JSON scene file containing the current world. No account is required. Keep it, share it, and reopen it later with Open scene from this computer. A JSON scene is editable model data; it is different from an exported image.
After signing in and verifying the account when required, save a named cloud world and optional description. When editing a previously saved world, choose whether to update it or save a separate copy. My Worlds can open, download, rename, or delete saved worlds.
Choose a BuildPhysics JSON scene file. A valid file replaces the current world, so save current work first. BuildPhysics validates imported scene data before loading it.
Downloads a PNG of the simulation view for worksheets, slides, or discussion. It is a picture only and cannot be reopened as an editable world; use Save Scene for that.
Sign in with an available provider or email/password to use cloud worlds. The menu then exposes My Worlds, verification when needed, account settings, and Sign Out. Local JSON saving remains available without an account.
Diagnostics is a technical self-test control shown only when diagnostics mode is enabled. Most users do not need it. If reporting a reproducible physics problem, diagnostics results can help identify whether the current browser passes the built-in checks.
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The in-sandbox Guide panel is experiment-specific: it shows an investigation question and three suggested steps. The small guidance card provides contextual instructions. Hide guidance collapses that help without changing the experiment.
This User Guide is the general reference for the entire application; the Guide panel is the activity prompt for the currently loaded experiment.
The Basic Tutorial introduces building, running, saving, resources, and loading. Advanced Tutorials provide hands-on practice with measurement and graphing, forces, surfaces, connections, friction, collisions, and beams. Interactive Lessons teach AP Physics 1 concepts through prepared models and questions. The Quick interface tour points out the primary controls without replacing the current experiment.
Use Back and Next to move through steps. A step number can jump directly to another step; the reload-step button reconstructs a lesson step when available. Skip bypasses a required verification, Exit closes the activity, and the −/+ button collapses or expands the card. On desktop, drag the tutorial header to reposition it.
Game mode presents staged physics challenges with a mission, charge objective, and restricted tools. Press Run before controlling the Pusher. Some stages provide one configurable rope, spring, disk, or block; their reset control lets you reposition that stage resource. Exit stage returns to the stage screen.
The bottom bar opens Create, Properties, Data, and More. More contains experiments, the activity Guide, lessons, tutorials, the quick tour, lab resources, saving, accounts, and settings/files. Large panels open one at a time. Landscape orientation gives more room for precise building, although the main controls remain functional in portrait.
Use More → Feedback to report a bug, request a feature, or describe confusing behavior. Include the experiment name, selected object, steps to reproduce, and the result you expected when reporting a technical issue.
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Choose New → Unit 8 · Fluids for a prepared experiment or a blank fluids world. The Fluids sandbox also appears in Build & Explore. Clicking New again returns you to the current activity in the library so you can browse nearby experiments.
The 14 prepared fluids experiments have Handouts on their library cards. Open Handouts to download the PDF or editable Word worksheet without loading the experiment. The toolbar Resources button opens the current activity guide and downloads. You can also find the Unit 8 lab webpages online. Blank workspaces have no prepared worksheet.
The Build panel groups tools into Objects & containers, Pressure & buoyancy, and Flow & outflow, with three buttons per row. Expand Supports & connections, Measurements, or Vectors for supporting tools. The four vector tools share one row. These groups remember whether you left them open or closed when you switch experiments.
Prepared scenes use the Fluids Lab background, with tank-bench, pipe-wall, or open-lab scenery. Background artwork does not create physical walls or a floor.
Add a Water tank from the object tools. Select it and drag its handles to resize width and height. Drag the waterline to change the fill level, including with a loaded piston attached. Fill-height input arrows change the value by 0.1 m. All tanks have a fixed front-to-back depth of 1 m.
Quick properties include liquid material, density, fill height, and Surface open to atmosphere. Turn that option off to show a lid and the air-pressure control. Set the enclosed air's absolute pressure, including values below atmospheric pressure or zero for an ideal vacuum. The gauge above the lid shows this setting. The setting is regulated; this model does not calculate trapped-gas compression.
The volume beside the left waterline is the tank space below the current liquid surface, including submerged objects. It rises when an object displaces water. The liquid inventory itself only changes when liquid enters, leaves, or overflows. All volumes use m³. A Scale can read newtons (the default) or kilograms; select the units in quick properties and drag its ends to change its width.
Blocks and disks start at 0.5 m front-to-back depth. Use the depth slider or numeric input to set a value between 0.01 m and the shared 1 m tank depth. Containers use a fixed perspective to show their depth. Blocks appear as rectangular prisms and disks as cylinders; their visible thickness follows the depth setting. The front face stays aligned with the measurement axes and resize handles. Fluids uses plain shapes instead of decorative block designs. The top-view depth comparison shows how much of the tank depth the object occupies.
Use Density and When resizing in quick properties to choose whether resizing keeps material density or mass fixed. The collapsible object information below Live values reports volume, density, submersion, buoyant force, and support readings. For an unattached object, Set floating position in quick properties or Fluid properties immediately prepares a static floating trial.
Liquid resistance in World slows an object's motion and rotation only while it is submerged, helping it settle at its resting waterline. It is on by default in buoyancy labs and new fluid sandboxes, and off in ideal pendulum and pipe-flow scenes. Turn it off to investigate sustained oscillations. Resistance is zero when the object is at rest relative to the liquid, so the final floating position still follows the balance between weight and buoyancy. The setting is saved with the scene.
Buoyancy is available as a force-vector option. Fluid force arrows share a smaller scale suitable for large forces. Velocity arrows and pressure-force displays start off in prepared fluids scenes. Sealed hollow hulls distinguish their outside displaced volume from shell material and enclosed air volume. Upright tanks can translate at constant velocity; this does not model sloshing or acceleration-induced surface tilt.
Drag a probe's tip to the measurement location. Quick properties switch between Absolute pressure (the default) and Gauge pressure. Gauge pressure is absolute pressure minus the environment's atmospheric pressure; in a closed tank's air it therefore measures the tank air pressure relative to the outside atmosphere. Inside liquid, the pressure includes the liquid above the tip. Absolute labels show one decimal place in kPa.
Probes also measure liquid in the manometer tubes and bottom bend. Equal-height points in the same connected static liquid have equal pressure. This does not imply equality between different liquids at arbitrary equal heights.
Choose Build → Flow & outflow → Flow speed probe, then click to place it anywhere. Drag its yellow sensing tip or meter head to sample a pipe, tank liquid, manometer liquid, or outlet jet. The arrow shows fluid direction and the label shows speed in m/s relative to the canvas. Stationary liquid reads zero; translating tank liquid includes the tank's velocity.
Jet readings include downward velocity as the liquid falls. While paused, a dashed predicted jet can be sampled; during a run, readings require emitted liquid at the tip. Outside liquid, the probe shows Outside modeled fluid instead of zero. Select the probe in Data and choose Flow speed to graph its reading over time, or use Record trial for a valid measurement. A Flow station remains the instrument for area, pressure, and Bernoulli energy comparisons.
Draw a pipe and drag its section handles to change its path. Drag the area handles at an end to widen or narrow the opening. Connect open ends by drawing from an end or bringing two ends together; connection targets are marked on the canvas. Flow stations are separate movable sensors, with their local cross-sectional area available in quick properties.
Set a volume flow rate and a valid reference pressure for an unbranched flow. The ideal incompressible model uses continuity and Bernoulli's equation to calculate speed and pressure along the pipe. The zero height level sets the gravitational energy reference. Tracer dots show motion without representing individual rigid droplets.
Open the separate Bernoulli energy graph window and choose a flow station. Move that station along the pipe to compare pressure, kinetic energy per volume, gravitational energy per volume, and their total. These bars use Pa (equivalently J/m³), not total energy in joules.
A fluid parcel follows a fixed amount of liquid. Its quantitative force explanation compares pressure force, weight, and acceleration on supported straight sections, including taper-wall pressure forces. Bends do not have the same straight-section explanation.
Attach an outlet to a tank and set its opening area and height. Fixed-head operation maintains the source level using an external supply. Finite-tank operation removes discharged liquid from the tank, so the level and outflow change. The jet follows an analytic projectile path; the coordinate x-axis does not stop it.
Place a collector in the jet's path to receive liquid. The shared volume account distinguishes liquid still in the source, liquid in flight, collected liquid, uncollected liquid, and any external supply. Jet range and flight time require a defined landing or collection condition.
Each manometer side has its own pressure mode: Atmosphere, Pressurized chamber, or Connect to another fluid. Chamber mode reveals an absolute-pressure input. Connected mode adds a hose and pressure sampling fitting: drag its cyan tip or metal body into a tank or pipe to measure pressure there. The tip marks the measurement point. Drag the instrument's handles to resize it. Each side shows its liquid height measured from the bottom.
Enable Second liquid on the left to add an immiscible lighter column, then set its density and height. The main liquid levels respond to both chamber pressures and this extra column. If liquid would leave the tube, the reading is out of range rather than a valid equilibrium measurement.
Layered tanks keep immiscible liquids separate with denser layers below lighter ones. Pressure adds the contribution of every layer above a probe. Pressure is continuous at an interface while its rate of increase with depth changes with density; buoyancy accounts for each displaced layer separately.
Select an object or instrument and choose Record trial to capture its current readings, including while paused. Change one setting, record another trial, and choose the comparison graph's axes. These manually recorded trials are separate from the ordinary time-sampled graph. The axis menus offer quantities present in the recorded rows, including settings such as area and density for parameter comparisons. A saved axis with no matching values is marked no recorded values. A quantity must exist in both selected columns for a trial to plot; unrelated instruments do not supply every measurement. Export the trial table as CSV for spreadsheet analysis; raw accounting measurements remain available in the export.
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Positive x points right and positive y points up. Vector angles are measured from +x. Positive angular displacement, velocity, acceleration, and torque are counterclockwise; negative values are clockwise.
Hiding force arrows, vectors, trails, labels, components, panels, or system totals changes only what is drawn. A physical effect is disabled only through a model input such as Gravity Enabled, the master Friction control, a zero force, a removed connection, or a changed object property.
Current scenes resolve contact values from least to most specific: World Conditions supplies the defaults, a surface can use custom values for its contacts, and custom settings for one exact contact win for that interaction. Restitution and friction follow the same hierarchy, with friction’s μs and μk controlled independently.
The former lower-value rule is retained only when loading older scenes: saved friction or restitution values from that version are converted into explicit custom contact settings. This preserves the old result without making the old rule apply to new contacts.
Ropes are massless and inextensible. A pulley is ideal and massless unless its mass switch is enabled. Springs follow the configured stiffness, relaxed length, and damping. Air resistance is absent when linear drag is zero. Contact friction is absent unless World friction or a custom friction setting enables it, and the master switch can temporarily disable all friction. The ground/contact energy convention is designed to match common AP Physics 1 point-mass treatment.
When a run begins, BuildPhysics captures the dynamic starting conditions. Reset restores that state while keeping the model settings used for the trial. To establish a different baseline, pause, reset if necessary, edit the setup, and begin a new run.
The vector sum of external forces controls translational acceleration. When rotation is available, the force’s application point also determines torque about the center or fixed pivot. Locking torque-driven rotation suppresses that rotational response and displays force arrows through the center of mass, while the same forces still contribute to translation.
The physics solver advances in 1/240-second steps. Playback Speed changes how quickly those steps are shown, not the equations. Trial measurements are recorded at 30 samples per simulated second, so graph tools operate on recorded samples rather than every solver step.
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Check Unit Limited Settings. A prepared early-unit experiment may intentionally hide later concepts. Turn the setting off or load a custom world to expose the full interface.
Pause the simulation first. Starting inputs and structure edits are locked during Run. Also confirm that the intended item—not a vector, joint, or overlapping object—is selected.
First confirm that the master Friction control is on and that the objects are actually in contact. Then inspect the most specific setting: Custom friction for this contact, the selected surface or conveyor’s custom coefficients, or the general coefficients. A zero coefficient at that level makes the contact frictionless. If Apply friction to is Custom settings only, add a custom setting wherever friction should act.
Select a body and run the simulation long enough to collect samples. Check that at least one graph series is enabled and compatible with the selected object. Reset clears the previous trial’s data.
Turn off Lock torque-driven rotation. Then make sure a force, contact, or gravity produces nonzero torque about the center or pivot. A force through the rotation point can change translation without creating torque.
Press Run first and move focus out of any form field. With gravity on, Up jumps only while supported and Down has no movement function. Use Left/Right for surface or airborne steering; with gravity off, all four directions fly.
Move the hook within Grab range of a movable object and press G. Fixed objects are not valid payloads. If the Puller is already carrying something, the next G press releases it rather than grabbing another object.
Use the site’s Feedback form for bugs and feature requests, or email contact@buildphysics.com. Include the exact button or field name so the question can be matched to this guide.
Try the exact button label, a shorter phrase, or a related term such as “spin” instead of “rotation.”