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Lesson plan · Grade 11 · 50 minutes

Collision Lab

I can show that total momentum is the same before and after every collision, explain where kinetic energy goes, and use impulse to design a safer collision.

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Standard
HS-PS2-2 NGSS
HS-PS2-3 NGSS
Shape
Explore first
Grouping
Pairs on devices, with whole-class debriefs.
You need
A device per pair. The tool on the projector. Notebooks or the class's digital lab notebook.
Tool
curioclass.org/tools/collision-lab/
  1. Hook5 min
  2. Explore18 min
  3. Make sense12 min
  4. Apply10 min
  5. Exit check5 min

Before class

  • Run the 5-minute start in the teacher notes yourself, so you know the Velcro and Steel numbers.
  • Turn Measurement noise off for the first runs. It goes on later.
  • Note that Spec 4 on the Spec sheet cannot be met. The teacher notes have the key; don't tell students.

Hook 5 min

  1. Ask: "Two shopping carts collide and stick together. Is anything conserved? Is anything lost?"
  2. Take a quick vote: momentum kept, energy kept, both, or neither. Write the tally on the board and leave it up.

Explore 18 min

  1. Pairs open Air Track, pick preset 1. Equal masses, spring and Launch. Record momentum and kinetic energy before and after in the ledger.
  2. Then preset 2. Equal masses, Velcro. "Momentum before and after?" (Both 0.150 kg·m/s.) "Kinetic energy kept?" (50 percent.)
  3. Turn on Predict and try preset 3. Heavy hits light. Pairs write both velocities before Launch unlocks.
  4. Pairs record runs with Spring, Rubber and Velcro in the Notebook, then turn on Measurement noise and record three more.
  5. Switch to Crumple Zone. Launch with Steel, then with Spring, and compare peak force and contact time.

Make sense 12 min

  1. Back to the vote on the board. "What stayed the same in every run, even with noise on?" (Total momentum.) "What changed from bumper to bumper?" (The kinetic energy kept.)
  2. "Velcro keeps no bounce, but momentum is still conserved. Where did the energy go?" (Into bending the bumper, sound and heat.)
  3. Show a Velcro run with Ride with center of mass ticked: the Total bar reads zero before and after.
  4. Put the two crumple graphs side by side. "Same shaded area, 1.00 N·s, but very different peaks. Why does a longer contact time mean a smaller force?" (Impulse is force times time. Stretch the time and the force drops.)

Apply 10 min

  1. Pairs open the Spec sheet, pick a spec, and design a Crumple nose that meets it.
  2. Every group that tries Spec 4 fails. Ask them to prove it can't be done: the crush force times the crush length has to be at least the kinetic energy.
  3. Connect to the real world: car crumple zones, bike helmets, airbags.

Exit check 5 min

On a card: "A 1.0 kg cart at 2.0 m/s hits a wall and stops. Design A stops it in 0.01 s, design B in 0.2 s. Find the impulse and the average force for each, and say which design is safer." (Impulse 2.0 N·s for both. 200 N for A, 10 N for B, so B is safer.)

Support and stretch

  • Support: keep to the Spring and Velcro presets. Fill in a ledger table with before, after and kept columns.
  • Support: let pairs use Slow motion and Jump to collision to watch the moment of contact.
  • Stretch: in the center of mass frame, Rubber keeps 36 percent of the kinetic energy (e squared). Derive why.
  • Stretch: with noise on, a Spring run can read more than 100 percent kinetic energy kept. "Can a collision make energy, or is this the measurement?"

Short on time

  • Do only Spring and Velcro on the Air Track (8 min).
  • Compare Steel and Spring in Crumple Zone (7 min).
  • Finish with the exit card (5 min).

How each button works is in the teacher notes. From Curio Class, free under CC BY 4.0: change it, print it, share it.