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Labs about proving the law of conservation of momentum

Overview The track will be used to create various collisions between the carts. The collisions will be arranged so that an initially moving cart will pass through a photo gate before hitting another object, so as to measure the initial velocity. After the collision, the cart will again pass through a photo gate so as to measure the final velocity. With these measured velocities, as well as the measured masses, the momentum and kinetic energy of the carts before and after the collisions can be calculated and compared.

Steps will be taken to deal with systematic errors in this experiment.

Simple Science Experiment: Conservation of Momentum with Marbles

The approximate effects of friction will be measured. Launchers are used so the initial conditions of consecutive trials can be reproduced.

Procedure for experiment A. Newtons First Law The object of this experiment is to test Newton's First Law, which states that an object will remain in its state of motion so long as no forces act upon the object. In this case, a cart moving with no friction would not change its velocity as it moves along the track. Place a cardboard strip between the two masses length wise so that it fits firmly.

  1. Maybe your mom stepped onto the board with you? Place the two weightless magnetic carts on the 50 cm mark from each end of the track.
  2. Steve Davala is a high school chemistry and physics teacher who likes to write and work with Photoshop. This means that when the velocities are both in the positive direction, the two carts are approaching each other from opposite directions.
  3. Do this by bringing the cart up to each of the photo gates and adjusting the height of bracket so that it is the cardboard that sets the timer off. A future experimental idea or change to the experimental design that might increase the overall accuracy of the lab would be to only push one cart towards another stationary cart for the elastic collision both carts are magnetic to simulate an elastic collision.
  4. Set the launcher to 3.

Do this by bringing the cart up to each of the photo gates and adjusting the height of bracket so that it is the cardboard that sets the timer off. You can adjust the height of the photo gate by turning the screw on the post and moving the bracket up or down. Make sure you adjust both of the photo gates.

You can adjust the compression by loosening the screw on the latching clamp and sliding it into position. Take one of the carts and bring it up to the launcher. Make sure that the cart's wheels are in the grooves of the track. Launch the cart by pulling the string on the launcher. Once it has passed through both of the photo gates, stop the cart and record the times displayed on the photo gates. Place a piece of cardboard into the groove on the friction block, you might need two to fit tightly.

Make sure you record the new mass of the cart. Procedure for Experiment A.

  1. Adjust the launcher to 3cm.
  2. Collision occurs in the graph above within the time frame of 1.
  3. The technology used in this lab was only so fast and could only pick up information related to an object's motion to a certain degree of accuracy. Inelastic collision with one object moving, with mass.

Elastic Collisions For this experiment, you will create elastic collisions with the two carts. You will explore all the possible scenarios; two carts of the same mass colliding, a cart of lower mass colliding with a cart of a higher mass, a cart of a higher mass colliding with one of a lower mass, and a cart colliding with an infinite mass the end stops.

It is important that you set the launchers to the settings described. These settings demonstrate each scenario best. Set the launcher to 3.

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Place the other cart with the friction block and the cardboard in position to be launched. Make sure that the carts' plungers are facing each other and that the plungers are all the way out.

The cart will pass through the photo gate and repel off of the stationary cart. The two carts will then pass through their respective photo gates. Record the initial time that the cart took to pass through the photo gate and the time the carts took to pass through the gates after the collision. Remember that the time displayed in memory is the total time.

Conservation of Momentum and Energy

You must subtract to get the actual second time. Set the launcher to 2cm. Adjust the launcher to 3cm. Move the photo gates to the opposite end of the track spaced the same way.

Slide the launcher to about 100cm from it's current position. Move the cart into position and launch it. Record the time displayed on both the photo gates before and after the collision. Inelastic Collisions This final collision experiment will deal with inelastic collisions. Repeat the procedure for part B, but this time the Velcro end of the carts should be facing front.

In each collision, the carts should collide and stick together. When the carts pass through the photo gate together, the beam will be broken only when the cardboard passes through. This means there will be a space where the beam is not severed, so make sure you measure the length of the two cardboard pieces and not the length of the two carts.

The instructions on how to do this experiment is in a hand-out which your TA will give to you.

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Data Analysis for Part A. This will be done by dividing the final value of the momentum by the initial, giving the fraction of the momentum that is conserved.

If the conservation laws hold, this should be equal to one. Results less than one indicate that momentum was lost. In the same way, the fraction of kinetic energy that is conserved will be found. Newton's First Law states that if there is no net force acting on an object, its momentum will not change.

Physics Lab - Conservation of momentum

Use the data you have recorded to test this by calculating the fraction of the momentum conserved in each trial. Because there is only one cart, its mass and length factor out of this ratio, which will then be 3.

Kinetic energy should also be conserved. To get a rough estimate of the effect this will have, calculate the average fraction of the initial energy and momentum lost for your data. To do this, first average all the momentum ratios and all the kinetic energy ratios calculated above, to get the average fractions conservedthen subtract these results from one to get the average fraction lost .