Hi, I'm Deysi from Design Squad, and I'm here with Eleanor and Reed and we're having fun with gravity.

Gravity is a force that is present in all things.

We use the invisible force of gravity to change the direction of speeding objects all the time.

NASA uses it too.

When a spacecraft passes a moon or a planet, they both exert a gravitational pull on one another.

NASA engineers use this gravitational pull to change the direction of a spacecraft, increase the speed, or both change the direction and increase the speed.

This is called a gravity assist.

Like gravity, magnets also exert an invisible force.

Our mission today is to use the invisible force of magnets to control how a ball rolls without ever touching the ball.

We've got a steel marble.

A magnet.

A paper cup that has a notch in it.

An index card... folded in half to act as our ramp, and this will be Mars.

ELEANOR: So let's put Mars maybe over here.

So then we would have to make this path instead of going straight, to curve like that.

So we're going to have to place the magnet somewhere to alter the course of this marble.

DAISY: We also have a piece of rope that we'll use to keep the ball from flying off the table.

REED: Maybe there.

ELEANOR: Yeah.

Can we try it?

Yup.

ELEANOR: No.

The magnet didn't really move the course of our steel ball.

Maybe we could move this a little closer.

So we don't want the ball to get too close to the magnet.

ELEANOR: Oh, that was close.

That moved it a little bit.

REED: That was pretty close.

What if we tried to do something with the magnet.

The steel ball tends to get attracted towards the middle of the magnet.

DAISY: A little too close.

We're getting there.

Oh, there it goes.

Wait, try it again.

There you go.

Good job.

(laughter) What I notice is that when the ball goes down the ramp, it always goes in a straight line unless a different force acts against it to slow it down or change its course.

That's actually Newton's First Law.

Now, we're going to change the direction of a rolling ball.

But this time the invisible force is stream of air coming from these... leaf blowers.

Make sure you get an adult's permission before you use a leaf blower.

Ready?

Goal!

For the directions on how to make this, and to see lots more activities related to NASA's missions, visit the Design Squad website.

Eleanor, are you ready?

Yes.

Reed, are you ready?

Yes.

Start your engines.

And go!