OBJECT:

To observe the relationship between an elastic body and the force of gravity upon it.

MATERIALS:

CAUTION:

This experiment has the potential of eye injury !! Be sure to wear your Safety Goggles at all times.

PVC ( Base from the SBB, you may have to place a few books, on each side of the Base for greater stability !) stand (two feet high) with a right angle ( the one used with the SBB ), two small rubber bands, one medium large rubber band, 3 paper clips, one metric ruler, pliers, small sandwich bags ( approximate size 6 1/2 inches X 5 1/2 inches X one inch, and marked with a marker, the number of pennies inside) with 5 pennies, 10 pennies, 20 pennies, 30 pennies, 40 pennies, 50 pennies, 100 pennies. A paper hole puncher.

Note:

How to make a punch hole in plastic bags, use a piece of paper above and below each layer of plastic you punch, in the case of the bags, there is an end flap, which makes up two layers, so be sure to use a small paper between the flap, and one piece above the flap and one piece below the flap.

PROCEDURE & OBSERVATION:

1. Obtain two small rubber bands, and slide them over the two foot PVC pipe stand, in such a way that they will not slide down; Space the rubber bands about 10 inches apart.

2. Now take a ruler place it against the two foot pipe, and try to slide the rubber bands over the ruler so that the rubber bands will hold up the ruler. ( See Fig 1 )

3. Now attach the right angle on top of the two foot pipe. ( with a small hole drilled, so that you can attach a paper clip to the right angle - like you did in the SBB )

4. After attaching the first paper clip to the right angle, then attach the second paper clip to this one, then attach a medium size rubber band ( in comparison to the small rubber bands ) to the paper clip.

5. Attach the third paper clip at the bottom of the rubber band, this paper clip is modified, in such a way, that the end of it makes roughly a 45° angle. To this 45° bend, make another bend one quarter of an inch at the end of this pointer, so the result will be a quarter inch horizontal pointer, that will enable you to read the cm off the ruler.

6. Take your plastic sandwich bag with 5 pennies and attach it to bottom paper clip, this will straighten out the rubber band. Now, adjust the height of the ruler so that the pointer of the paper clip is at the edge of the ruler.

7. Replace the five penney bag weight with 10 penney bag and record how far the pointer moved. _______ cm

8. chart

Chart

# of pennies	10	20	30	40	50	60	70	80	90	100
Total cm
cm change

9. Find out how many cm does the rubber band stretch every time an increase is made by 10 pennies and record your answer into the chart.

QUESTIONS:

1. Define Force -

2. Define Matter -

3. Define gravity -

4. What are the units for Force ? ______

5. For every 10 pennies of weight you have added; did the pointer drop the same number of cm ? _________

6. Suppose you had an unknown weight ( like a large bolt and nut, or a socket from a socket wrench ), do you think that you could find its known weight ?

7. Obtain an unknown weight and see how many cm does the pointer drops ( stretches ) ______ cm = ________ g

8. Take a rubber band and as you stretch it, place it next to your cheek. Does it feel warm ? Where did this heat come from ?

9. Stretch a rubber band for about 15 seconds. As you let the rubber band contract, place it next to your cheek. Does it feel cool ? _____ Why do you think this happened

10. Do you think that you could have used a spring scale for the above experiment ?____ Explain your answer.

Note:

This was a demonstration of Hooke's Law!

Hooke's law states that within the limits of a perfect elasticity, strain is directly proportional to stress.

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