PHY 2048L
Lab 5

Ballistic Pendulum and Projectile Motion

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Updated: 1/21/2013
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We will be doing"Lab 13", MOSTLY as described in the lab manual.

Guiding Question:

You measure two speeds, so be sure to explain which one you consider to be the best estimate of the ball's speed, and why.

Preparing for the lab:

Read the theory for "Lab 13" (pages 137 to 139) in the lab manual before answering the questions on LON-CAPA.

Comments

Attention to safety is important in this lab. The steel ball is fired at about 15 mph, which is 22 feet per second. It will damage things in its path and can definitely put an eye out. Do not stand in the line of fire at any time. The catch box can be used as a safety shield (see below) during the first part of the lab, but the ball will be fired off the end of the table during the second part of the lab. Check the line of fire before shooting.

Some operational suggestions: There is a knurled ring that adjusts the spring tension. Be sure it is tightened before starting your work or your results will be inconsistent. Check that the pendulum is swinging freely and properly aligned. ( I check the setup before and after each lab, but you should do so as well.) Don't mess with it until you have done the first set of measurements. Measure the mass of the pendulum after making the ballistic pendulum measurements (part one) and reinstall it like you found it.

Do not cock the gun until ready to fire, and do not fire it too rapidly. The springs appear to weaken if not allowed to 'rest' between firings. Try to make every shot under the same conditions in both part 1 and part 2 of the lab.

I have modified the second part of the lab as described in a handout.

You will predict where the ball should land and mark that landing area on the paper used as a target. The distribution of landing points provide a sort of histogram that will show both random errors (the scatter of the points), which you can compare to your predicted error band, and systematic errors (location of centroid compared to your predicted landing point) in a very visual fashion. However, you still need to do the calculations for part 2 so you can answer the post-lab questions.


Apparatus

initial arrangement of ballistic pendulum and catcher box

Photo of the ballistic pendulum and catcher box arranged the way you should find them when you arrive. The knurled adjustment ring I mention above can be seen on the left, just to the right of the knob you pull to cock the gun.

ballistic pendulum and catcher box in use

This photo shows the system as it looks while in use with the catcher box on the floor. The basic arrangement is to have the box as far as it will go against the wall, and then position the launcher at the predicted distance from a landing point near the center of the box. You will probably want the entire system closer to the edge of the table to make it easier to measure down to the floor.

 
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