Krampf
Experiment of the Week
- Swing Time
http://www.krampf.com
For this week's experiment, I thought we would look into
something that none of us seem to have enough of. Time. This experiment
will not give you any extra time, but it will let you use up some time
in learning how to measure it, without a watch.
Imagine that you are out in the woods, or on a deserted island, or in a
hotel room in Buffalo. You want to time how many seconds it takes for
something to happen, but you do not have a clock. Could you make an
accurate device which would let you count the seconds?
For this experiment, you will need:
* a key
* a piece of string about 40 inches long
Tie the key to one end of the string. Now measure 39 inches from the
end of the key and tie a knot in the string at that point. If you do
not have a yardstick on your desert island (or in your hotel room), you
can do what I did and use a sheet of 8 1/2 x 11 paper. That is the
standard size for typing paper. Twice its length and twice its width
give the right length for your pendulum. (8.5 + 8.5 + 11 + 11 = 39)
Now, hold the string at the knot and let the key swing freely. Hold
your hand very still, or tie the string to something. I used the floor
lamp in the hotel room. Pull the key to one side and release it. It
will swing back and forth. Each swing, from one side to the other will
take one second. I timed my pendulum with the stopwatch on my laptop
computer and found it to be very accurate. After three minutes, when
the pendulum was barely moving, it was still accurate to the second
with the stopwatch.
The length of the pendulum controls how long it takes for the key to
swing back and forth. It does not matter how heavy the weight is or how
far back you pull it. A brick and a key will each take one second per
swing on a 39 inch long pendulum. What if you wanted to make a pendulum
that would swing from side to side in half a second? How long a string
would you need? Should it be longer or shorter? How much longer or
shorter? Try it and see. I will tell you that the length will probably
not be what you expect it to be.
After trying this experiment, you should now know why grandfather
clocks are so tall. The pendulum on a grandfather clock is 39 inches
long, swinging back and forth to keep track of the seconds.
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