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Bouncing Ball Gravity Lab

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About This MicroSim

This lab is the "hello world" of interactive simulation: one ball, one floor, and two rules. Every frame, gravity is added to the ball's downward speed and the speed moves the ball. When the ball reaches the floor, its speed is reversed and multiplied by the bounciness, so it keeps only a fraction of its speed. A readout panel shows the ball's height, its speed in pixels per frame, the number of bounces, and the height of the first bounce as a percentage of the drop. Dashed lines mark the drop height and the first bounce peak, and a faint dotted trail shows the last 40 positions of the ball.

With Predict first turned on, the lab will not let you simply watch. Each time you change a slider, it pauses and asks whether the next bounce will be higher, lower, or the same. After you answer, the next drop reveals the result and explains it. The comparison is surprising for many learners: gravity changes how fast the ball falls and rebounds, but not how high it bounces, because each bounce keeps bounciness² of the height.

Learning objective: The learner will explain how changing gravity and bounciness changes the motion of a falling ball, by predicting an outcome and then testing it.

Bloom's taxonomy level: Understand (verb: explain)

How to Use

  1. Press Start to drop the ball. Watch the readout and the dashed line that marks the first bounce peak.
  2. Move the Gravity or Bounciness slider. With Predict first checked, the lab pauses and asks for your prediction.
  3. Choose Higher, Lower or Same, then press Start or Drop Again.
  4. When the ball reaches the top of its first bounce, the panel tells you whether you were right and why. The purple dashed line shows the bounce before your change.
  5. Uncheck Predict first to explore freely; the sliders then change the motion immediately.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/microsims/sims/bouncing-ball-gravity-lab/main.html"
        height="502px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Audience

Teachers, instructional designers, learning-technology developers and learning-analytics practitioners (college undergraduate and professional development). No physics background is assumed.

Duration

15 minutes

Prerequisites

  • The idea of a variable that changes over time (height, speed)
  • The definition of an interactive simulation: a model plus immediate interaction

Activities

  1. Predict (3 min): Before touching the lab, write down what you expect to happen to the first bounce if gravity is doubled. Then write down what you expect if bounciness drops from 0.80 to 0.60.
  2. Test (5 min): Use the lab with Predict first on. Change one slider at a time and record your prediction and the result for at least four changes, including one gravity change and one bounciness change.
  3. Explain (5 min): In pairs, explain why doubling gravity made the ball move faster but left the first bounce at the same height. Use the two rules shown in the panel under "The model" in your explanation.
  4. Connect (2 min): Discuss which learner actions in this lab would count as evidence of understanding if the lab were instrumented (for example, a correct prediction on the first try versus random slider movement).

Assessment

  • The learner correctly predicts the direction of change for a new bounciness value.
  • The learner explains in one or two sentences why a change in gravity does not change the bounce height, referring to the fraction of speed kept at the floor.
  • The learner can state what the bounciness value represents (the fraction of speed kept after each bounce).

References

  1. Coefficient of restitution - Wikipedia. The physics name for "bounciness": the ratio of rebound speed to impact speed.
  2. Free fall - Wikipedia. Motion under constant gravitational acceleration, the model used between bounces.
  3. p5.js createSlider() reference - p5.js. The built-in slider control used for gravity and bounciness.
  4. PhET Interactive Simulations - University of Colorado Boulder. A large library of research-based science simulations.