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Go over the concept of acceleration and gravity so that the students
have a working understanding of it in relationship to dropping something
from a height.
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Go over safety precautions: Be extremely careful when dropping the
objects out the window. Make sure there are no passersby who might be
hit. Be sure that objects won't hit anything that can be broken on the
ground, or near ground level, such as a ground floor window. Do not lean
your upper body out of the window.
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Position one responsible student at the ground floor, (outside) after
making the socked penny balls and having cut the soda bottle. This will
be a group experiment as a class.
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Put 150 pennies in the toe of one of the socks and tie it off with
string so that you have a compact ball of pennies. Put the remaining 50
pennies in the other sock, and tie it off. Cut off the excess material
from each sock. Wrap each ball of pennies thoroughly and tightly with
duct tape, so that the surface of each ball is completely covered by
several layers of tape. (When you are done you should have two solid
lumps of pennies, tightly wrapped, one three times as large and heavy as
the other.
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Cut the liter soda bottle about 2 inches above the darkened support
plastic at the bottom of the bottle. Carefully using the scissors, punch
holes near the rim. Cut four pieces of string, each about 6 inches long
and tie one through each of the holes. Tie the free ends of the strings
together in the center above the container, knotting them securely. Tie
the end of one of the balls of string tightly to this central knot,
making sure that it will not come loose.
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Position one person in a window 2 to 3 stories above ground level.
The window should be above the grass if at all possible, and the drop
area should be free of any obstructions.
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The responsible person outside at the ground level should be
positioned below the window in a place with a full view of the other
person, but not in danger of being hit by an object falling straight
down.
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The person in the window should hold one end of the free ball of
string and drop the ball out the window. The person on the ground should
mark the string where it hits the ground. This is the distance the
object will fall.
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The person upstairs should carefully lower the plastic container to
the ground, and tie the other end of the string to some heavy object in
the room. This can be used to return the fallen object to the person
upstairs, for repeated drops.
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Have the students write down a hypothesis about the relative rate at
which the two penny-roll objects will fall to the earth. Will they reach
the ground at the same time? Or will one fall faster?
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Holding one object in each hand, the person upstairs should drop the
two objects simultaneously from exactly the same height above the window
ledge. The person on the ground, while standing well clear of where the
objects will land, should note when they hit the ground. Write down
whether the classes' results confirm or contradict their hypothesis.
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Now choose one of the objects to use for the rest of the experiment,
and drop it from the window. Make sure that the object is dropped
straight down. Do not throw the object down, up or out. Simply release
it from your grasp. Upon release the person on the ground should start
the stopwatch and stop it when the object hits the ground. Practice this
dropping and timing until fairly consistent times are achieved.
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After practicing the release and timing and reaching a consistent
time, do four trials and record the time for each on a piece of paper.
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Measure the length of string that stretched from the window to the
ground (the first string) using the yardstick. Record the distance.
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Once the times of the falls and the distance of the falls have been
found, the acceleration due to gravity can be found using this formula:
g = 2d/t (squared) where g = acceleration, d = distance and t = time.
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Calculate the rate of acceleration for each of the time trials.
Average the results by adding the four values of g and dividing by four.
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