Colliding Trolleys Practical

Investigating Collisions


Momentum is the quantity of the motion of a moving object. If an object is at rest/not moving, then it does not have momentum. It can be calculated using the formula below:

Momentum (kg m/s) = Mass (kg) x Velocity (m/s)


To investigate whether momentum is conserved during a collision.


- Two dynamics trolleys

- Electronic balance

- Metre ruler

- 30cm ruler

- Several 1kg masses

- Two rubber bands

- Level bench top

- A4 paper

-Masking tape


- A piece of A4 paper was attached to the bench with masking tape. Two parallel lines on the paper, 20cm apart, were ruled.

- Two trolleys were linked with the rubber bands.

- The trolleys were pulled apart and held with their front ends on the two lines.

- The trolleys were released. They accelerated towards each other and collided at the same time. How far the trolleys traveled in a given time was proportional to their velocities. The collision point was determined and marked on the piece of paper.

- The distance was measured from one line to the collision point and the same for the other line. Because the trolleys both collided at the same time, there was no need to measure the times because the distances were proportional to the collision speeds.

- Various masses were added to one or both of the trolleys and the experiment was repeated.


m1 = 0.2kg

d1 = 0.1m

m1 x d1 = 0.02

m2 = 0.2kg

d2 = 0.1m

m2 x d2 = 0.02

(m1 x d1) - (m2 x d2)

= 0 momentum


When the trolleys were released, they travelled towards each other for the same period of time, unless there was a weight on one rather than the other. Then, the speed of each trolley would have changed, therefore the trolleys would not travel for the same period of time. Since the trolleys have the same mass and acceleration, the magnitude of the force acting on each trolley is the same. In addition, the final total momentum was zero, since according to the law of the conservation of momentum, the total momentum before the movement of an object is the same as the momentum after the movement of the object. Since the momentum for both trolleys is the same, the momentum is zero. So the initial total momentum of the whole 'system' was zero.


In conclusion, the motion of the two trolleys proved that when there was no weight added to them and the collision point was the same/in the middle, the law of the conservation of momentum proved true in this experiment. The momentum before the movement of an object is the same as the momentum after the movement of the object.