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 near the bottom of Create lists selectable items in the current scene. Choosing one selects the same item in the world and opens Properties. This is useful when objects overlap or a small connection is difficult to click.
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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.
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.
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.
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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.
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.
Copy duplicates supported bodies, surfaces, pulleys, and displacement measurements with a small offset. Connections are not automatically duplicated with a copied body. Delete removes the selected item and any connections that depend on it. The floating × in the world performs the same deletion.
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. A surface can either Use World collision settings or override restitution for contacts with that surface. A specific contact-pair override is most specific and wins over the surface 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.
Friction must first be enabled globally with the Friction Enabled switch. World friction supplies the default μs and μk for contacts. A surface can either Use World friction or set its own coefficients. A specific contact-pair Override friction is most specific and wins over the surface and world defaults. Bodies use the world defaults unless a contact-pair override is defined.
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 pair overrides 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 conveyors, elevators, and moving tracks. In the surface’s collision settings, choose whether to use the world friction and collision defaults or override them for contacts with that surface. A contact-pair override still takes priority.
Select a body or surface and open Properties → Contact overrides to customize one interaction. Choose Add contact override, select the other item under Interaction with…, then enable Override restitution, Override friction, 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. Pair overrides are saved with the scene. A surface’s Use World collision settings and Use World friction choices control its material defaults before any pair override is applied.
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.
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.
This global switch enables the friction model for contacts. World friction supplies the default static and kinetic coefficients when a surface is set to Use World friction and no contact-pair override is present. Individual coefficient fields can be edited while friction is off, but no friction force is applied until the switch is on. The friction-force display becomes available with the model.
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.
These controls change visualization only. They do not add forces or alter motion.
Snap vectors while editing snaps an arrow within 8° 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, and acceleration 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 and recent-samples table focus on the currently selected object. 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.
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. Use it when exact numbers are more useful than a graph. For the full recorded dataset, choose Export CSV.
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 the collected values for spreadsheet analysis. Select and run the bodies you want recorded 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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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, Friction Enabled, 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 override those defaults for contacts with that surface, and a contact-pair override wins for one exact 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 pair overrides. 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 Friction Enabled is checked. 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.
Confirm that Friction Enabled is checked and the objects are actually in contact. Then inspect the most specific setting: a contact-pair Override friction, the selected surface’s μs and μk override, or the World friction defaults. A zero coefficient at that level makes the contact frictionless. If the surface is set to Use World friction, edit the world values instead of the surface card.
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.”