Collisions Prac


AIM - To investigate whether total momentum is conserved during a collision

INTRODUCTION: Momentum, collision

A collision occurs when a person or an object struck violently against each other. Momentum describes a mass of an object in motion and is measured in kg m/s. Every object that is moving has momentum and can be calculated using mass x velocity.


Two dynamics trolleys Electronic balance Metre ruler

Several 1 kg masses to add to the trolleys

Two rubber bands tied together that will stretch to 20 cm quite easily

Level benchtop Piece of A4 paper Masking tape


  1. The piece of A4 paper was placed onto bench top with masking tape. Two parallel lines on the paper, 20 cm apart were ruled.
  2. The two trolleys with the rubber bands were placed together.

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

  4. The trolleys were released. The trolleys accelerated towards each other and collided at the same time.
    How far the trolleys traveled in a given time is proportional to their relative velocities. Determine where the trolleys collide and mark the collision point on the paper.

  5. 5 Measure the distance from one line to the collision point (d1) and the same for the other line (d2). Because the trolleys both collide at the same time, there is no need to measure the times because the distances are proportional to the collision speeds.

  6. 6 Add various masses to one (or both) of the trolleys and repeat the experiment. Test approximately five different mass combinations.


RESULTS m1 = 200g = 0.2kg
d1 (in m) 0.01
m1×d = 0.02
m2 = 200g 0.2kg (total in kg)
d2 (in m) 0.1m
(m1 × d1) – (m2 × d2) = 0kg


When the trolleys are released, they travel towards each other at the same period of time because they have the same weight. The magnitude of the force acting on each trolley is the same because of the same mass both trolleys have and the acceleration If both trolleys come to a stop after the collision, the final total momentum of the ‘system’ was zero because they both started at a zero momentum and finished at zero momentum.

According to the last column of results the initial total momentum of the ‘system’ was zero due to the law of conservation of matter which states that the momentum must be conserved before and after the experiment.

CONCLUSION - The experiment demonstrated that momentum before and after the experiment will be equal.

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