PHY 2048L
Lab 1

Uniformly Accelerated Motion

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Updated: 1/21/2013
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We will be doing the experiment described as "Lab 5" starting on page 53 of the lab manual by Loyd.

Guiding Question:

Remember that a correct answer to a question like this must have an uncertainty and units, and (to be complete) should also comment on its accuracy and precision. Your abstract can contain other information (such as the angle of the table), but it must give a clear and complete answer to the guiding question for your report to earn full points.

Preparing for the lab

Read the background information on pages 43 and 44 (theory for "Lab 4", which we are not doing)along with the theory and instructions for "Lab 5" (pages 53 to 55 in the lab manual) before answering the questions on LON-CAPA. You should also review the material concerning the Basic Lab Skills we will use.

Be sure you allow enough time to do the required calculations. It is a really good idea to do the linear least-squares fit (the fourth problem on LON-CAPA) before you leave Lab Zero. If not, you can use some of the computers in the Learning Commons to do the required fit with "Logger Pro".

Lecture

The first thing you will be asked each week is to tell me what the objective of the lab is and what you are going to do. This will give you guidance on what should be at the start of the abstract for the lab report due next week.

This week we will review the basic physics of what acceleration to expect on an inclined plane, and some very important details on how to use the equipment and how to do the calculations.

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 pulsed DC, so you are advised to avoid touching the puck itself or the carbon paper on the table 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.

Your value for g came out to be 0.1 m/s2? You must be careful when using Graphical Analysis. The calculation tables in our lab manual are almost always arranged so that the last column contains the independent variable (the one that we plot on the abscissa, i.e. on the "x" axis), right after the dependent one (the one we plot on the ordinant, i.e. on the "y" axis). Unfortunately, this is exactly the opposite of the order you need to enter them into Graphical Analysis. If you are careful to rename your data columns as "t" and "v" by following the steps given in the instructions handout, then you are more likely to notice an error when you look at your graph.


Apparatus

We will plug the computer into the wall outlet at the inside end of the table (you can see it at the far left edge 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 timer.

air compressor, air table with pucks, wood block, rulers

(Not shown: large balance for measuring the mass of the puck and computer used to run Graphical Analysis.) The black object on the far left corner of the air table is a foot switch (which you can also operate by hand) that turns on the high voltage for the spark timer as long as it is held closed. Practice getting this timing right before taking data.

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.