PURPOSE:
To expose the student to new equipment and lab procedures. And to determine the angular momentum of an object through data analysis.

INTRODUCTION:
Objects executing motion around a point possess a quantity called angular momentum. This is an important physical quantity because all experimental evidence indicates that angular momentum is rigorously conserved in our Universe: it can be transferred, but it cannot be created or destroyed. The following is the relationship between moment of inertia and rotational velocity:

L = I w

where angular momentum (L) is equal to the product of moment of inertia (I) and angular velocity (w). Since angular momentum is conserved:

L = I_i w_i = I_f w_f

where i is initial an f is final. In this lab you will be dealing with solid metal disks that rotate about their center. The moment of inertia for a disk is:

I = 1/2 mr₂

where m is he mass of the disk in kg, and r is the radius in meters. The equation for angular momentum of a disk can be written as:

L = 1/2mr²_Disk1 w_Disk1 = 1/2mr²_{Disk 1+Disk2} w_Disk1+Disk2

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The angular velocity of your rotating objects is determined by a sensor wheel that rides on the surface of your disks and is displayed on a small meter.

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The objects that you will be measuring, angular velocity / mass / radius, are 2 metal disks.

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The two disks rotate on a nearly frictionless bearing. Compressed air is pumped into an "air bearing" where the main platform rides on a cushion of air.

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If you get into trouble and perform some procedure that causes the lab to fail(lab equipment will no longer operate), you can press the "Reset" button and the simulation will return to the starting position.

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PROCEDURE:

1) You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted)

ROOM 1:

2) In this room, Disk 1 is already in place on an "air bearing", a device that provides a nearly frictionless means to rotate the disk. Click on the right side of the red pump located on the table. This forces compressed air into the air bearing and provides a cushion for Disk 1 to ride on. To the left side of Disk 1 is displayed its mass. Record this mass. Grab the left side of Disk 1 and drag it to the right, release and start it rotating.

3) On the table is a meter that displays angular velocity sent by a wheel sensor on the shelf. Turn on the meter by clicking on the red button on its face. The sensor is not in contact with the rotating disk and thus the meter displays the value 0.000 rad/seconds. Slide the sensor wheel to the left until it makes contact with the rotating disk. Record the angular velocity of Disk 1 as shown on the meter.

4) Pick up Disk 2 from the table and set it on the rotating Disk 1. Record the angular velocity of the combined Disk 1 and Disk 2. Move to Room 2.

ROOM 2:

5) Record the mass of Disk 1. Place Disk 2 on the balance and record its mass. Spin Disk1 and record its angular velocity as you did in procedure # 2-3 above.

6) The meter in this room is old and in bad shape thus it can only display the angular velocity of Disk 1 BUT SHOULD NOT BE USED TO DISPLAY THE ANGULAR VELOCITY OF THE COMBINED DISK1 & DISK 2. Move to Room 3.

ROOM 3:

7) Record the mass (kg), radius (m) and angular velocity (rad/s) of the Disk found on the table using the equipment on hand.

8) Calculate the requested values asked for on the lab sheet and any given by your teacher. For help on these values click on the "Special" button and select "View Data & Hints". Select "File Report" to send a copy to be viewed by your teacher.