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Phys 105L - Physical Science Lab 2 - Levers - 4 September 2008 Background

In 220 BC Archimedes, a Greek scientist and philosopher, said "Give me a me a place to stand and with a lever long enough I can move the whole world." This statement is in reference to the power of simple machines, one type of which you will examining in this lab. A simple machine is a device that has few or no moving parts. Its job is to help provide mechanical advantage by a change of direction and/or magnitude of the forces applied. What is meant by mechanical

advantage is the number of times a simple machine multiples the force that you apply to do a job. For example, you cannot apply sufficient force to pull a nail out of a board with your bare hands, but using a claw hammer as a lever you can remove the nail. Simple machines include the lever, the inclined plane, the screw, the pulley and the wheel. In this lab we will be examining a firstclass lever how it can provide mechanical advantage.

A first-class lever is one in which the fulcrum (pivot point) is located between the effort and the resistance (the input and the output, respectively). For example, think of teeter-totter or see-saw found on a playground. As you push down on one end of the lever (effort), the load (resistance) goes up on the other end.

Procedure

in this experiment, you will create a working first-class lever by using a meter stick, a wooden wedge as a fulcrum, and a set of pennies for units of weight. You will need a set of 25 -30 pennies (cups of pennies are provided by the instructor). Check that all of your pennies were minted after 1982 to insure that they all have the same mass.

Part A. Scientific Method State a question. The first step in the scientific method is finding a question that you want to answer. Several possible examples related to levers might be; How does a lever work? How can a lever adjusted to increase the mechanical advantage? How quickly can we expect the

mechanical advantage to increase? How much can one lift with a lever? · · Tape your fulcrum to the benchtop so that it is secure. Now balance the flat side to the meter stick on the fulcrum with the centimeter side up. Where do you expect the fulcrum to balance the meter stick? Were you correct in your prediction?

·

Form a hypothesis: What do you think? Have you had any previous experience with levers? Can you make a prediction of how a lever will act when the experimental

conditions are changed? Play with your lever by adjusting the placement of the fulcrum and changing the weights on either end. After a little bit of experimentation, form your hypothesis, and educated guess of what you would expect to happen to the fulcrum point as you change the number and/or positions of the pennies. Write a 2-3 sentence summary of your hypothesis on the report sheet. · Do the experiment: After you have made your hypothesis statement, test it by changing only one variable at a time and observing what effect it has on the experiment.

Part B. Num ber of pennies versus Position of fulcrum · · Remove all pennies from the meter stick and rebalance it on the fulcrum. Record the position of the fulcrum to the nearest tenth of a centimeter on your report sheet. · Next, add one penny to the very end of the meter stick (lay the penny flat covering the last centimeter) and rebalance the meter stick on the fulcrum. Record the position of the fulcrum to the nearest tenth of a centimeter on your report sheet. · Add another penny to the same side of the meter stick and again move the fulcrum point until the meter stick is rebalanced. Record the position of the fulcrum to the nearest tenth of a centimeter on your report sheet. · Repeat the previous step until you have reached 25 pennies on the end of the meter stick. For each penny you add, record the position of the fulcrum to the nearest tenth of a centimeter on your report sheet. · Lastly, make a stack of pennies as high as you can on one end of the meter stick and find the balance point. Record the number of pennies used and the position of the fulcrum to the nearest tenth of a centimeter on your report sheet.

Part C. Data Analysis Now you have a generated a set of data that you can analyze. It may be difficult to see the trend by visual inspection. But, if you were to graph the data, the trend would become easier to see and predictions for future experiments could be made. · Keeping in mind the conventions of graph-making you learned last week, make a graph of the number of pennies versus the position of the fulcrum point. Remember that the independent variable (the one you control) goes on the x-axis and the dependent variable goes on the y-axis. · Now plot a graph of the number of pennies versus the change in fulcrum position.

Pre-Lab Quiz (1 point) Name What is the fulcrum of a lever?

Lab 2 - Levers

4 September 2008 Mailbox #

What is a scientific hypothesis?

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EXPERIMENT 1

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