PURPOSE:
To expose the student to new equipment and lab procedures. And to calculate the centripetal acceleration acting upon an object.

INTRODUCTION:
An object accelerates if its velocity changes. Because velocity is a vector quantity, acceleration occurs whenever the speed or direction of an object changes. The acceleration of a turning or orbiting object is known as centripetal acceleration (a_c).A swinging stopper apparatus(see below) can be used to verify that the centripetal acceleration is equal to the square of the velocity of the stopper in its circular path divided by the radius of the circle.

A_c = v² / r

Since a_c is constant for an object rotating at uniform speed, the ratio v² to r should be constant.The force to keep the object orbiting is called centripetal force (F_c), without it, the object would discontinue accelerating and move in a straight line (i.e.: it is not forced out but forced to continue in a circular path!)

F_c = m A_c

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A stopper of known mass is rotated in a circle of known radius producing a centripetal force that matches the force produced by a known(brass) mass and gravity.

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Two brass weights and a rubber stopper will provide the masses needed to complete this lab. An electronic balance will mass the objects.

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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)

2) Place the large brass weight, small brass weight and rubber stopper, one at a time, on the electronic balance and record their individual masses.

3) Click on the black button on the tape measure and pull out the yellow tape. Click on the now red button to lock the tape in place. On the table is a length of string with a loop at each end. The string extends through a glass tube which will be used to hold the string apparatus once in motion. There is a green and red piece of tape on the string indicating two distinct distances. Measure the distance from the left end of the string(include the loop) to the right side of the green piece of tape and record in meters! Do the same for the distance to the red piece of tape and record in meters. Now measure the length of the glass tube and record in meters. Take the length to the green tape and subtract the length of the glass tube and add 0.09m. A rubber stopper will be attached to the left end of the string and it has a constant length of 0.09 meters. Record this calculated length as the radius to the green marker. Do the same for the length to the red marker and record as the radius to the red marker.

4) Click on the glass tube, to pick it up, and center the tube in the middle of the screen. Pick up the large brass weight and hook it to the loop below the green and red markers. A collar on the string will prevent the weight from pulling the string out of the tube. Pick up the stopper and hook it to the loop at the other end of the string.

5) Located at the lower left hand of the screen is a pair of buttons that will cause the stopper to rotate about the glass tube. (the program didn't think that you could handle rotating the stopper at a constant velocity!) As you click on the up arrow, the horizontal portion of the string lengthens and the vertical portion shortens. Adjust the rotation until the green tape just meets the bottom of the glass tube. The revolutions per second (RPS) will be displayed. Record this value. Adjust the rotation until the red marker just touches the bottom of the tube and record the RPS. If you wish, you can check the radius of the rotating stopper and string with the tape measure to see if your calculated radius matches.

6) Adjust the rotation until it stops. Remove the stopper and then the brass weight. Hook the small brass weight to the string and then the stopper. Repeat Procedure #5 above recording the two RPS values now using the small weight.

7) 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.