# Conservation of Momentum Practical Write Up

AIM: To investigate if momentum is conserved in two-dimensional interactions within an isolated system.

HYPOTHESIS: Without the effects of friction the momentum will be conserved in the isolated system. In all three experiments the momentum before the interaction will equal the momentum after the interaction.

METHOD: An air hockey table was set up and a video camera on a tripod was placed over the air hockey table. The camera was positioned so it was directly above the air hockey table facing downwards. The air hockey table was turned on and two near identical pucks were placed on the table, one at one end of the table and one in the centre. The puck at the end of the table was launched by hand towards the other puck which was stationary. On impact the first puck continued in motion and initiated the motion of the second puck. The collision was filmed on the video camera. After this a second experiment was set up with the same two pucks, but this time they were placed in either corner of the air hockey table. They were launched at the same time into the centre of the table, where they collided and bounced off each other and this collision was also filmed. In the final experiment the two pucks were replaced with larger pucks with Velcro around the edges. Like the previous experiment the two pucks were placed in two of the corners of the table and launched at the same time towards the centre. Due to the Velcro the pucks stuck together when they collided and they both continued in the same direction, and this was filmed. The films of the collisions were put onto a computer and they were analysed frame by frame.

RESULTS:

EXPERIMENT 1:

EXPERIMENT 2:

EXPERIMENT 3:

DISCUSSION: The overlayed images of the pucks on the air hockey table show the progression of the pucks and the effect the collision had on them. Momentum is found by using the equation where p is momentum, m is mass and v is velocity. The law of the conservation of momentum states that i.e. the total momentum of an isolated system is conserved. To discover if momentum has been conserved vector diagrams can be drawn. In experiment 1 and 2, is the momentum of the black puck and is the momentum of the red puck.

EXPERIMENT 1:

The first experiment is where the red puck is initially stationary and the black puck is launched into it and then rebounds off at an angle. As the red puck is initially stationary, i.e. the initial momentum is 0; the total initial momentum (pTi) consists entirely of the momentum from the black puck, hence . By using vector addition it is evident that so momentum is conserved.

EXPERIMENT 2:

In experiment 2 both the black and red puck are initially moving and they collide in the centre of the air hockey table where they rebound and move away from each other. As both pucks are initially moving their total combined momentum is equal to the total initial momentum, i.e. . By using vector addition the total initial momentum is equal in magnitude and direction to the total final momentum. This shows that momentum is conserved.

EXPERIMENT 3:

For the final experiment the two pucks had Velcro around the edge, so when they collided in the centre they stuck together. As both pucks are initially moving the total initial momentum can be found by adding the initial momentum of both pucks, i.e. . After the collision the pucks stick together and continue 'as one', this means that the total final momentum only consists of one object. However as the mass of this object is doubled, the momentum is also doubled. This means that the vector for the total final momentum must be doubled in length. Through the use of vector addition it can be seen that momentum is conserved as the total initial momentum is equal in both magnitude and direction to the total final momentum.

ERRORS: There were many random and systematic errors that could have occurred in this experiment. A random error...

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