PHY 2048L
Lab 2

Projectile Motion on the Air Table

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Updated: 1/21/2013
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We will be doing "Lab 6", which starts on page 63 of the lab manual.

Guiding Question:

IMPORTANT: Be sure you support your answer with quantitative data from your experiment, such as the answer to post-lab question 4 or the percent difference between the two accelerations you measured.

Preparing for the lab:

Read the theory and instructions for "Lab 6" (pages 63 to 65 in the lab manual). You might also review the physics of 2-D motion in Chapter 3 of the Wolfson textbook used in the lecture class. Be sure to review the material concerning the Basic Lab Skills we will use, primarily the use of Logger Pro like we did last week as well as the meaning of "accuracy" and "precision".

Like last week, this lab uses an air table to produce a low friction environment, but in this lab we will use its unique features to study projectile motion in two dimensions. Your experience last week makes this lab easier, but take a look at the information below in conjunction with the procedure on pages 64 and 65 to get a better feeling for what we are going to do.

Caution

It is very important that you do not touch the hoses with your hands unless absolutely necessary. The oil from your hands will speed the degradation of the latex rubber used in the hoses. Use the handle between the puck and the hose.

The sparks are created by high voltage DC, so you are advised to avoid touching the puck itself while the spark timer is in operation.

The top of the air table is glass. Do not break it.

Comments

I will check for entanglements and that the electrical connection is good between the supply and the puck. You will need to do a trial run to be sure you are getting a spark as well as some dry runs to get a feel for when to start and stop the timer. It is very important that you start the timer just after the puck is released (a simultaneous start is not necessary) and turn it off before the puck reaches the bottom (marks after it bounces back will leave a very confusing trace on the paper).

We only have one balance that can measure the mass of the puck. This is kept on the front desk, but should be used at your lab station. Do not remove the puck from the hose to measure its mass. Carefully put the balance on your (level) air table or just behind it so you can put the puck on it with the hose attached. Protect the black carbon sheet with a sheet of cardboard or some printer paper before putting the balance on the air table. Because the big balance has to be shared, you might want to wait and measure the puck mass after all of your measurements are done.

Read the instructions for the data analysis carefully, and remember what was done in a lecture example during the first week of class. The delta-x value and the velocity calculated from it are associated with a time midway between the start and end of the interval. The time column in your calculation table should contain entries such as 0.05, 0.15, 0.25, etc. The rows in the tables are aligned with delta-x midway vertically between the x values you calculate it from to try to make this more obvious to you. Also note that you divide delta-x by delta-t, not by t. Big difference.


Apparatus

We will plug the computer into the wall outlet at the inside end of the table (hidden by the box of tiles on the far right side of the picture), and plug everything else into the power bar you can see on the front edge of the table. This way the on/off switch of the power bar will control the (very noisy) air compressor and spark timer without affecting the computer. You only turn on the power bar when you need the air pressure and spark timer.

air table with pucks, rulers and protractor, air compressor, tiles

(Not shown: large balance for measuring the mass of the puck and computer used to run Graphical Analysis.) You can see the black rectangular "foot switch" (which you usually operate by hand) just to the right of the table. This switch turns on the high voltage for the spark timer while it is held closed. Practice getting this timing right before taking data.

Details

Tilting the Table:
We will not use the wooden block from the inclined plane experiment because the resulting "vertical" acceleration cannot be optimized. Instead, we have a box of ceramic tiles that can be used in combination to create a suitable angle. This picture shows five tiles in use, but you can use more or fewer during your practice runs until you are comfortable with the parabolic path you get. I don't think it will work very well with less than four. tiles used to elevate the table

A sheet of blank newsprint (not shown) will go on top of the black paper to record your data. The details of how this is done, and other comments about the setup, are shown on a separate page. Remember that the marks appear on the bottom of the paper, and be sure to make a note on the paper of which end was up.

 
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 ?? Contact me if you have any questions.