Collision Carts

Explore conservation of momentum

  1. Choose magnetic bumpers for a perfectly elastic collision or hook-and-loop pads for a perfectly inelastic collision.
  2. Set each cart’s total mass and starting velocity. Positive velocity points right; negative velocity points left.
  3. Launch the carts. Pause, advance one frame, or use slow motion to inspect the collision.
  4. Turn on velocity and momentum vectors. Arrow direction shows the sign; length shows magnitude. Momentum depends on both mass and velocity.
  5. Reset to replay. Changing the setup also resets the track. Try the same setup in both collision modes.

Total momentum stays constant during the cart-to-cart collision. Kinetic energy stays constant only in the elastic mode. A zero-length vector appears as a dot.

Ideal model: level frictionless track, one-dimensional motion, instantaneous collision. The run pauses before either cart reaches an end stop, where an external impulse would change the carts’ total momentum.

02 / OBSERVE THE MOTION

Low-friction dynamics track

MAGNETIC BUMPERS
LEVEL TRACK / 4.0 m+ RIGHT →
Two dynamics carts on an aluminum laboratory trackA blue cart and an orange cart carry removable steel masses. Optional arrows show their current velocities and momenta.01234 mALUMINUM DYNAMICS TRACK · ADJUSTABLE LEVELING FEET
READY TO LAUNCH0.00 s
SHOW VECTORSSeparate scales · p = mv
Cart A velocity
Cart B velocity
Total momentum
Kinetic energy

Set up the carts, then launch. Watch how motion transfers from one cart to the other.

Physics behind the simulation

For elastic collisions, v′A = [(mA − mB)vA + 2mBvB] / (mA + mB), with the corresponding expression for B. For perfectly inelastic collisions both carts move together at (mAvA + mBvB) / (mA + mB). Total momentum is signed; kinetic energy is ½mv² summed over both carts.

The magnetic bumpers model a perfectly elastic interaction; hook-and-loop pads model sticking. Real equipment has rolling resistance and some energy loss. The collision is instantaneous in this ideal model; vector lengths change immediately at impact. The run ends before end-stop contact.