Mechanics
Inelastic collision
Watch kinetic energy drop as the balls barely bounce.
Inelastic collision — interactive Mechanics simulation. Watch kinetic energy drop as the balls barely bounce. Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Inelastic collisions
In an inelastic collision, kinetic energy is not conserved. Objects may stick together or move off slower than in an elastic case.
Momentum is still conserved if external forces are negligible, but some kinetic energy becomes internal energy (deformation, heat). Low restitution makes the collision visibly “sticky.”
- Σp_before = Σp_after
- KE_after < KE_before
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
A moving ball crashes into a heavier stationary ball and they move off together. Is momentum conserved even though kinetic energy is lost?
Predictions to weigh
- Both momentum and kinetic energy are conserved
- Momentum is conserved, but kinetic energy is not
- Neither momentum nor kinetic energy is conserved
Variable roles
What you set:
- Mass of ball A m₁ (kg)
- Mass of ball B m₂ (kg)
- Initial speed of ball A v₁ (m/s)
What you measure:
- Initial momentum p = m₁v₁ (kg·m/s)
- Combined speed after collision (m/s)
How the investigation runs
- Open the inelastic collision simulation and press Reset.
- Enable the KE probes on ball A and ball B.
- Set ball A's initial speed for each trial below, press Play, and record the shared speed both balls move at right after they collide.
Governing equation
Momentum — p = m·v
The quantity conserved in every collision, including this one. Ball B starts at rest, so the system's total momentum before impact is just ball A's momentum m₁v₁.
Kinetic Energy — KE = ½·m·v²
Unlike momentum, kinetic energy is not conserved in an inelastic collision — comparing the total KE before and after the collision shows how much energy was lost to deformation and heat.
What the printable worksheet asks students to work out
- Show your work computing the initial momentum p = m₁v₁ for one trial and compare it to the simulation's readout at the same trial.
- Using the total mass (m₁ + m₂) and momentum conservation, predict the final speed and compare it to your recorded value. How close is the match?
Where this shows up beyond the lab
- Compute the kinetic energy just before the collision and just after (using the combined final speed and total mass). Where did the missing kinetic energy go?
- This collision isn't perfectly inelastic (restitution ≈ 0.05, not exactly 0). Would you expect the real final speed to be slightly higher or lower than the ideal prediction? Explain.
- AP Physics 1 — Unit 3: Work, Energy, and Power
- AP Physics C: Mechanics — Unit 3: Work, Energy, and Power
- IB Physics — A.3 Work, energy and power
- General High School Physics — Work, energy & power
- NGSS High School Physics — Energy accounting in systems
- Middle School Physical Science — Newton's third law and collisions
- Middle School Physical Science — Kinetic energy
- Welcome to Collision Inelastic
- Press Play
- Select the ball
- Energy lost
- Open the data
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.