Our heroes are in a dilemma. They've
been kidnapped and locked in identical
rooms and left with only a radio and
three science experiments. One of the
rooms is falling down an enormous mine
shaft, while the other is in deep space.
Their captors have promised to release
them if they can tell which is which.
Try their three experiments - will your
findings help them?
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Stand on a bathroom scale and notice
where the needle stops. Watch the needle
as you quickly squat down. It will
wobble, but which way does it go first?
Try this a few times to be sure of your
observations. Hint: A digital scale probably won't work for this.
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| Incoming transmission... A. "I can't really stand on the scale, but okay, I got it - nope, no reading, it's a zero." B. "I don't think my scale works. When I stand on it, nothing happens. No, wait, when I squeeze it with my hands the needle moves, so it must be working. So why won't it measure my weight?" | |
| What does a Slinky look like when you
hold it high in the air by one end? Drop
it while you watch and listen as it
falls. What do you notice? Try this with
a friend and take turns dropping and
watching the Slinky. Hint: You'll need to shorten your Slinky for this activity by winding tape around two thirds of it.
|
 |
Incoming transmission... A. "Hey, I found a Slinky here, but something's wrong with it. It's all bunched up, even if I hold it by one end." B. "My Slinky's weird too. I can stretch it out, but it snaps shut as soon as I let go. I can't get it to stretch out when I hold one end." |
|
What happens when you drop a leaky
bottle? To find out, poke a hole in the
side of a plastic bottle. Hold your
finger over the hole while you fill the
bottle with water. Uncover the hole.
What do you think is pushing out the
water? Now, hold the bottle high and let
go. Repeat this several times and pay
close attention to what happens. Do you
think your results will be similar to
the results of our hero in the falling
room or our hero in deep space? What happens to the stream of water if you jump into the air while holding the bottle? What happens when you toss the bottle into the air? (Be careful not to spin the bottle.) Hint: This is a wet activity, so do it outside or in the bathtub. Also, ask an adult to help you poke the hole in the bottle. Make the hole first with a straight pin, followed by a pencil point. >plastic bottle >water >pin >pencil |
|
| Incoming transmission...
A. "I just poked a hole in the side of
the bottle, but no water is coming out.
I don't understand. Is this real water?" B. "OK, I'm ready to try mine. Huh! Same results. When I hold the bottle, nothing comes out. When I drop it, it doesn't even fall_it just hangs in mid air. What's going on?" | |
| (1) So what was happening while you watched your weight? Gravity is constantly pulling us against whatever we're standing or sitting on. A chair supports you and keeps you from falling. If the chair suddenly disappears, you fall toward Earth. For the split second you are falling, you are in a condition known as free fall. Here's what is happening: Objects fall as a result of Earth's gravity. When gravity is the only force affecting an object's fall_such as when you fall out of a chair_we describe the condition as free fall. | (2) When you stood on the bathroom
scale, it supported your weight. When
you squatted quickly, for a brief
instant you approached free fall and
seemed to have no weight. That's why the
reading quickly dropped. A similar thing
happened with the Slinky. As you
supported one end, you became the force
that was working against gravity. When
you let go, you took away that force.
The Slinky fell and its springiness
snapped it shut. While you were holding the leaky bottle, gravity was pulling both the bottle and water toward Earth, but only the water was falling. Its weight pushed it out of the bottle. When you dropped the bottle, both the water and bottle were in free fall. Water stopped flowing because, for a brief moment, it was weightless. |
| (3)
Why did the water stop squirting when you
tossed the bottle and when you jumped?
Even though the bottle was going up, it and the water were still in a state of free fall because they were no longer supported by anything. The effects of being in free fall are identical to the effects of being in deep space. What does this mean for our heroes? Alas, they are destined to spend their days in their locked rooms. Without outside information, no experiment they can perform in their rooms will distinguish between deep space and free fall. |
(4) What if one of our heroes was in a room in near space, such as Earth orbit? Orbits, like most space travel, are a type of free fall. Many people think that astronauts are weightless because there is no gravity in space, but this is far from true. Gravity is everywhere in our universe. Most things we think of as weightless_such as Space Shuttle astronauts_are that way because they are in free fall. (When in orbit around Earth, the Space Shuttle is constantly falling around the planet. It never hits the ground because it is moving forward and its curving fall follows the curve of the Earth.) Understanding free fall is the key to understanding weightlessness. |
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