PURPOSE:
To expose the student to new equipment and lab procedures. And to observe the mechanical advantage generated by pulleys.

INTRODUCTION:
A pulley is a rotating wheel with a groove between two flanges around its circumference. The groove normally locates a rope, cable or belt. Pulleys are used to change the direction of an applied force or realize a mechanical advantage. In example A below, a pulley is used to change direction of the force applied and gives no Mechanical Advantage(MA=1). In examples B and C, the top pulley changes the direction of the force but the other pulleys increase the mechanical advantage of the force applied. In example B the Ideal Mechanical Advantage(IMA) = 2, and in C the IMA = 3. An easy way to determine the IMA of the set-up is by counting the number of ropes supporting the mass to be lifted. The force applied by the hand in A equals the force of the hanging mass (F = m x g). In B the applied force is 1/2 of the hanging mass's force and in C it is 1/3. Although it appears that we are getting a free ride in energy as the mechanical advantage increases, work dictates otherwise. Work = F x distance. In B the rope has to be pulled down a distance twice that which the weight goes up. In C, you guessed it, the rope has to be pulled down a distance 3 times that of the weight. So even though the force needed decreases, the distance through which it has to be applied increases. The work done in all three examples is the same.

The IMA indicates the ideal relationship between the force applied and the force pulling at the other end. In reality, friction and the mass of the pulleys have to be accounted for. The Actual Mechanical Advantage(AMA) is normally less than the IMA and has to be determined experimentally. During this lab you will measure the force needed to lift a weight, distances that the applied force & weight force traveled, the IMA, the AMA and the work done on the weight.

---*---

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.

---*---

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 can on the loop in the end of the string hanging from the left pulley. Pick up the unknown weight and place it on the electronic balance. Record its mass in KILOGRAMS. This weight is called unknown because each lab has a different value. Hang the weight on the loop on the right string. The can that you attached is made of light aluminum and, with the aide of gravity, is still not enough to lift the weight.

3) Click the black button on the tape measure, located on the table(the button should turn red). Now drag the tape upwards until it meets with the horizontal support bar. Click on the red button to lock the tape in place. Move the extended tape over and measure the distance from the table to the bottom of the hanging can. Record this value in METERS. Move the tape over to the right out of way.

4) Pick up the red container marked "BBs" and hold the left lip, above the center of the hanging can. While holding it there press the "p" key to start to pour BBs into the can. The little BBs will flow out at a fast rate so the program will keep track of their added mass to the can and stop the pouring when the combined mass of the can & BBs overcomes the force of the weight.

5) Now that the weight has been pulled to the top of its run, take the tape and measure from the table to the bottom of the weight. Record this value in meters.

6) Drag the can over to the balance and record the mass of the can & BBs within. Record this value in kilograms.

If you foul up or wish to run the lab again, press the Reset button.

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.