Elastic and inelastic collisions
One collision: track where both momentum and energy go.
In a one-dimensional collision the total momentum is always conserved. Whether kinetic energy is conserved depends on the coefficient of restitution e: the speed of separation after the collision divided by the speed of approach before it. e = 1 is a perfectly elastic collision with no loss of kinetic energy; 0 < e < 1 is an inelastic collision, in which part of the kinetic energy becomes internal energy; e = 0 is a perfectly inelastic collision: the objects stick together and move at a common velocity, losing the most kinetic energy.
Velocities vs. time
The velocities jump at the moment of collision; when e = 0, the two lines coincide afterwards.
Think about it
If the objects stick together (e = 0), what fraction of the initial kinetic energy is lost?
m₂ / (m₁ + m₂): half when the masses are equal, and more the heavier the object that is hit. In general the fraction is (1 − e²)·m₂ / (m₁ + m₂), which is zero when e = 1. Set e to 0, then change m₂ and watch “KE lost in collision”.
Model assumptionsHorizontal, frictionless · instantaneous collision · object 2 starts at rest · collides at 2 s · 5 s loop · positive to the right
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.