Ok, sort of a silly experiment I admit. But here’s what we’re going for – there is an invisible force acting on you and the ball. As you will see in later lessons, things don’t change the way they are moving unless a force acts on them. When you jump, the force that we call gravity pulled you back to Earth. When you throw a ball, something invisible acted on the ball forcing it to slow down, turn around, and come back down. Without that force field, you and your ball would be heading out to space right now!
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Here’s what you need:

• you
• the Earth (or any planet that’s convenient)
• a ball

Download Student Worksheet & Exercises

Here’s what you do:

1. Jump!
2. Carefully observe whether or not you come back down.
3. Take the ball and throw it up.
4. Again, watch carefully. Does it come down?

Gravity is probably the force field you are most familiar with. If you’ve ever dropped something on your foot you are painfully aware of this field! Even though we have known about this field for a looooong time, it still remains the most mysterious field of the four.

What we do know is that all bodies, from small atoms and molecules to gigantic stars, have a gravitational field. The more massive the body, the larger its gravitational field. As we said earlier, gravity is a very weak force, so a body really has to be quite massive (like moon or planet size) before it has much of a gravitational field. We also know that gravity fields are not choosy. They will attract anything to them.

All types of bodies, from poodles to Pluto, will will attract and be attracted to any other type of body. One of the strangest things about gravity is that it is only an attractive force. Gravity, as far as we can tell, only pulls things towards it. It does not push things away. All the other forces are both attractive (pull things towards them) and repulsive (push things away). (Gravity will be covered more deeply in a later lesson.)

Exercises 

1. What did you determine about gravity and how it affects the rate of falling?
2. Did changing the object affect the rate of falling? Why or why not?
3. Did changing the variable affect the rate of falling?  Why or why not?

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Advanced students: Download your Gravitational Force Lab here.

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Click here to go to next lesson on Inertia.