Teacher Demonstration
Use the live model as a shared screen demonstration before students try their own predictions and observations.
Physics / Newtonian Mechanics
Plane Rigid Pendulum
Explore Plane Rigid Pendulum as an interactive EJS simulation for mechanics.
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1. Watch or Launch
Launch the Interactive
Open the simulation, adjust the controls, and compare what changes on screen before answering the concept-check questions.
2. Big Ideas
Key idea Circular motion requires a resultant force toward the centre of the path. The object may move at constant speed, but its velocity changes direction, so it is accelerating centripetally.
What Students Can Learn
- Distinguish speed from velocity in circular motion.
- Identify the centre-seeking direction of centripetal acceleration.
- Relate larger speed or smaller radius to greater centripetal force demand.
- Use force direction to explain why circular motion is not force-free motion.
Guiding Question
If speed is constant, why is the object still accelerating?
3. Try the Investigation
Trace the Direction
Pause or inspect the motion and identify the instantaneous velocity direction.
Locate the Centre
Identify the direction from the object to the centre of the circular path.
Change Speed or Radius
Compare how the required centripetal force changes.
Explain Direction Change
Use velocity direction change to explain centripetal acceleration.
4. Teacher Notes
Lesson Use
Use this to address the misconception that constant speed means no acceleration.
Discussion Prompts
Ask: Where does resultant force point? What would happen if that force disappeared?
Teaching Moves
Have students draw tangent velocity arrows and inward acceleration arrows at several positions.
5. Concept Check
These questions are generated from the topic and the concept illustrated by the simulation. Use them after students have explored the model.
Concept Score
Correct first attempts build a streak and unlock higher point multipliers on this device.
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Answer each question once to build your streak.
1. In uniform circular motion, where does centripetal acceleration point?
2. Why can an object accelerate while its speed is constant?
3. What happens to required centripetal force if speed increases at the same radius?
4. What is the velocity direction at an instant in circular motion?
5. What would happen if the inward resultant force vanished?
Expert Challenge
Unlocks after 3 correct concept-check answers on this page.
1. In a pendulum interactive, where is speed usually greatest and what evidence should be used?
2. What is the best expert feedback for 'the pendulum turns around because tension pushes it sideways'?
3. If the model lets length change, what should students compare?
4. What is the expert response to 'larger amplitude always means a much shorter period'?
5. What makes a pendulum conclusion expert-level?
7. Learning Pulse
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