Use a Meter stick as Scale!

Materials-

* Meter stick

* string

* various unknown masses

* balance for checking accuracy

A meter stick can be used as a scale as long as you know the mass of the stick. You can think of it as a miniature seesaw with only one person on it. Just as a person can use a seesaw alone as long as he sits with the pivot close to him as seen in figure 1, the mass of a meter stick can be used to balance an attached mass. In the below situation, when finding the lever arm for the seesaw, you should measure the distance from the pivot of the entire system to the CG of the seesaw alone (see figure 1 below)

Answer the following questions before beginning the lab.

1. Where is the center of gravity of a meter stick?

2. If a meter stick has a weight hanging from the side at the 0 cm mark, where would you expect the center of gravity to be for the meter stick-weight system? (Hint: don’t give a specific number as your answer, give a range on the meter stick).

3. If you added a heavier weight to the same side, how would this affect the CG of the meter stick-weight system? If the CG is in a new position, which way does it go, toward the 0 or the 100 cm mark? Explain your answer.

4. If the seesaw in figure 1 was less massive, how would the location of the balance point change?

5. If the seesaw in the picture weighs 30 kg, what does the boy weigh? Show work.

Use the following directions for the lab portion.

1. Get a meter stick of known mass and write the mass in the chart on the other side of this sheet.

2. Find CG of meter stick with two finger method (Should be at .5 m).

3. Hang an unknown mass from the end of the meter stick with a piece of string.

4. Find CG of unknown-meter stick system. Record it in chart.

5. Use your knowledge of torque to find mass of unknown.

6. Check your work with a scale.

7. Find percent error (directions in back of black lab book page 320).

Fill in the following Chart

What do you think could have caused any error you had? Give three reasons.

Would this method work on another planet, and give you the same readings? Why or why not? Explain your answer in a couple of complete sentences.

E-Mail

Rick Sarringhaus

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