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Unit 1: Mechanics Page 24
Experiment: Detecting the you’ve ever dropped something on
Gravitational Field your foot you are painfully aware
of this field! Even though we have
Here’s what we’re going for – there known about this field for a
is an invisible force acting on you looooong time, it still remains the
and the ball. As you will see in most mysterious field of the four.
later lessons, things don’t change
the way they are moving unless a What we do know is that all bodies,
force acts on them. When you from small atoms and molecules to
jump, the force that we call gravity gigantic stars, have a gravitational
pulled you back to Earth. When field. The more massive the body,
you throw a ball, something the larger its gravitational field. As
invisible acted on the ball forcing it we said earlier, gravity is a very
to slow down, turn around, and weak force, so a body really has to
come back down. Without that be quite massive (like moon or
force field, you and your ball would planet size) before it has much of a
be heading out to space right now! gravitational field. We also know
that gravity fields are not choosy.
Here’s what you need: You, the They will attract anything to them.
Earth (or any planet that’s All types of bodies, from poodles to
convenient), and a ball.
Pluto, will attract and be attracted
Here’s what you do: to any other type of body. One of
the strangest things about gravity
1. Jump! is that it is only an attractive force.
2. Carefully observe whether or not
you come back down. Gravity, as far as we can tell, only
3. Take the ball and throw it up. pulls things towards it. It does not
4. Again, watch carefully. Does it push things away. All the other
come down? forces are both attractive (pull
things towards them) and repulsive
Gravity is probably the force field (push things away). (Gravity will
you are most familiar with. If be covered more deeply in a later
lesson.)
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