To investigate Whether the total momentum is conserved during a collisions


Momentum is a vector quantity that describes the motion of a moving body, and is calculated with the formula: Momentum (kg m/s) = Mass (kg) x Velocity (m/s). The law of conservation of momentum states that the total momentum of a closed system does not change; meaning that when two object collide, the total momentum before the collision equals the total momentum after the collision.


- 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.

4) 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.

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 )

M1= 0.400kg

M2= 0.300kg

D= 20cm

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

= 0.02


As the trollies had different weights attached, they travelled at different speeds; the lighter trolly was able to travel faster than the heavier one due to the variating amount force needed to pull the two trollies. The magnitude of the force needed was dependent on the mass and the quantity of the force.

After the collision, both trollies remained at rest leaving the final momentum at zero, as they were not moving. The initial momentum, however, was measured at 0.02kg m/s due to the differences in weight.


In conclusion, this experiment was able to demonstrate the law of conservation of momentum by showing the momentum for before and after a collision remain equal unless the objects have mass differences. :)