Colliding Trolleys


To investigate whether total momentum is conserved during a collision.


The momentum in a collision can be calculated with the

formula: Momentum (kg m/s) = Mass (kg) x Velocity (m/s) Momentum is a vector quantity that describes the motion of a moving object and indicates how much force is required to stop an object. The Law of Conservation of Momentum states that The total momentum before an event is equal to the total momentum after an event.


  • Two dynamic trolleys
  • Electronic balance
  • Meter ruler
  • Ruler
  • Several 1KG masses to add to the trolleys
  • 2 x Rubber bands
  • Level bench top
  • Piece of A4 paper
  • Masking tape


1) Attach the piece of A4 paper to the bench top with masking tape. Rule two parallel lines on the paper, 20 cm apart.

2) Link the two trolleys with the rubber bands.
3) Pull the trolleys apart and hold them with their front ends on the two lines.
Release the trolleys. The trolleys will accelerate towards each other and collide at the same time. How far the trolleys travel travel in a given time is proportional to their relative velocities.
4) Determine where the trolleys collide and mark the collision point on the paper.
5) Measure the distance from one line to the collision point, and the same for the other one. Because the trollies collide at the same time, there is no need to measure the time because distances are proportional to the collisions.
6) Add various masses to one (or both) of the trollies and repeat the experiment. Test five different weight combinations


( m1 x d ) - ( m2 x d )

= ( 0.4 kg x 0.2 m ) - ( 0.3 kg x 0.2 m )

= 0.02


When the trollies were released, they traveled towards each other at different speeds and therefor different distances. The lighter trolly traveled faster and covered more ground than the heavier trolly. There are different magnitudes of force acting on each body as there is a direct correction to it mass and the amount of force on a object. As the trollies both came to a stop after the collision, the final total momentum of the 'system' was 0 kg m/s. The initial momentum of the 'system' was 0.02 kg m/s. The experiment could be improved by being more consistent, for example, the strength in which the trollies were pulled back with.


The experiment demonstrated that the momentum before and after a collision is the same