PURPOSE:
To expose the student to new equipment and lab procedures. And to observe Pascal's law in action.

INTRODUCTION:
Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container. A prime example is the hydraulic brakes of an automobile. When you press on the brake pedal, that same pressure is applied to the brake mechanism in your car. Even though the brakes are several feet away, a fluid filled line can curve and bend it way to this brake and will carry the same pressure that was applied to the other end of the line. This is true because liquids, such as brake fluid, are incompressible and when pressure is applied, it is transmitted completely(almost) without any compression of the liquid molecules themselves.

In the diagram below we see a system that has a small piston, "A", and a large piston, "B", set in a water filled chamber. If we apply a downward force to A, the pressure generated would be

Pressure_{at A}= Force_A/Area_A

That pressure would be transmitted to piston B and

Pressure_{at A}= Pressure_{at B}= Force_B/Area_B

because of Pascal's law. Putting these two equations together:

F_A / A_A = F_B / A_B

We can see that the area of A is much smaller than the area of B, thus to keep the equality the force on B must be greater than the force on A. This feature is utilized by hydraulic jacks where a small piston (with a small force) pushes up a large piston (with a large force). You should realize that the small piston, in the diagram below, has to travel a large distance downward to make the large piston move upward a little distance. So the trade off is a small force travels a large distance to move a large force a short distance. You will be testing this statement in this experiment.

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This is the set up to test Pascal's law. On the left is a small diameter hypodermic and on the right, a large hypo. The two are connected by a nonflexible tube willed with water. Each have been fitted with a platform connected to their plungers.

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The can, which will be filled with BBs, and the unknown weight will supply the mass during this lab. The masses, with the help of gravity, will produce the forces applied to each hypodermic.

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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) Pick up the ruler and measure the diameter of each hypodermic. Record these values in METERS! Measure the distance the small and large hypodermic plungers travel up and down. Note: while holding the ruler, press "p" to rotate. You can grab the plungers and move them freely. Record these values in meters.

3) Place the can on top of the small hypo's platform attached to the top of the plunger. Place the unknown weight on top of the large hypo.

4) Pick up the BB can and hold the left lip over and above the center of the can. While holding it there, press the "p" key to pour out the BBs. Since the BBs come out quickly, the program will stop their flow at the point where the small hypo's plunger starts to move.

5) Place the can, now containing some BBs, on the electronic balance and record the mass in KILOGRAMS.

6) 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.