Measure the motion
Connect radius and period with the speed around a circular path.
AP Physics 1 · Unit 2, Part 2 · Circular Motion and Gravity
Circular Motion
Observe a circular trip and test how speed, radius, and mass change the acceleration and inward force needed to keep turning.
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Start guided lesson
Learn by doing
Three ideas you’ll put into motion
Track the directions
Compare the tangent velocity with the inward acceleration.
Change one variable
Test how speed, radius, or mass changes the required inward force.
The big idea
The key ideas, at a glance.
Turning changes velocity
Even at constant speed, changing direction requires an acceleration toward the center: ar = v2/r.
Centripetal describes the net force
The inward net force is mv2/r. It comes from real interactions, such as tension, gravity, or contact forces.
A quick comparison
Double the speed while keeping radius and mass fixed.
Required inward force becomes four times as large.
Teaching this topic?Classroom fit, AP connections, and support
- Classroom fit
- Use for a concept introduction, guided independent practice, or a projected class discussion.
- Before students begin
- Velocity vectors, Newton’s second law, and the circumference of a circle.
- Built-in support
- Prepared scenes, guided prompts, and feedback on lesson questions.
- AP Physics 1 connections
- Unit 2: circular motion, radial acceleration, and net force.
- Check for understanding
- Ask why constant speed does not guarantee zero acceleration.
- Optional extension
- Compare more trials in the Uniform Circular Motion lab.
Ready to test your thinking?
The first scene is set up. Start the lesson and explore.