This Week's Experiment - #317 Action and Reaction
This week's experiment comes from my hotel room. I was sitting at the desk,
thinking of ideas for experiments. As I sat, I swiveled back and forth in
the chair. As I swung back and forth, I decided that it would make an
interesting experiment. You will need:
a chair that will let you spin around
pillows or other weights that will not cause damage if you throw them
Start by placing the chair in an open space, with plenty of clearance in all
directions. This will prevent broken lamps and e-mails to me from upset
parents. Sit in the chair and lift your feet off the ground. Now, without
touching the floor, the base of the chair, or other objects, try to get the
chair to turn. Not very easy, right? With some experimentation, you
should be able to get it to move some. If you twist the upper part of your
body quickly to the right, the chair should turn slightly to the left. If
you twist back to the left, the chair should turn to the right.
Next, get a heavy pillow or something similar. Again, making sure that your
chair can turn easily, hold the pillow away from your body. Holding your
arm straight, swing the pillow from the side and release it. As you throw
the pillow in one direction, your chair should turn in the other direction.
Try this again with something heavier. I used a bag of laundry. The
heavier the weight that you throw, the more your chair should spin. Also,
the farther you throw the weight, the more you will turn.
Why does this happen? There are some very basic laws that govern how things
move. Isaac Newton boiled them down into three basic laws. Newton's third
law of motion tells us that for every force, there will be an equal force in
the opposite direction. As you saw when you first tried to get the chair to
turn, you need something to push against. If you can push against the
floor, it is easy. As you push against the floor, an equal amount of force
pushes you away, turning the chair.
The same thing happens when you twist your body. As your muscles push your
upper body to the right, they also push your lower body to the left.
Instead of pushing against the floor, you are pushing against your own body.
In the same way, when you throw the pillow in one direction, an equal amount
of force pushes you in the opposite direction. That is why throwing a
heavier weight makes you spin more. The more force it takes for you to
throw the pillow, the more force you get to push you in the opposite
direction.
Since a heavier weight takes more force to move it, what would happen if we
used a very heavy object, like a refrigerator? Do not try to throw the
refrigerator across the room. Instead, move your chair near your
refrigerator. Sitting in the chair, reach out and push against the
refrigerator. What happens? Your chair turns, but the refrigerator stays
still.
If there is an equal force in both directions, why doesn't the refrigerator
move too? With your chair beside the refrigerator, reach out and place your
hand against it. Use a tiny amount of pressure to push against it.
Nothing happens. Neither you nor the refrigerator moves. As you push a
little harder, you will reach the point where your chair begins to move. At
that point, there is enough force in your direction to move the chair, but
not enough force in the opposite direction to move the refrigerator. I
tried making the refrigerator lighter by removing some of the ice cream, but
it did not seem to make a difference in my results. Even after I added the
weight of the ice cream to my body, the results were still the same, but you
might want to try it yourself, just to make sure.
Have a good week.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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