Joan Cartan Hansen: Gravity is the force of action between two objects, in this case between the melons and the earth.

To talk about gravity you first have to talk about mass and matter. Now matter takes up space and has mass and mass is a measurement of how much matter something has. The more something weighs the more mass it has and the more gravity pulls on it.

Your body has mass and so does your friends so there is a gravitational pull between them.

Oh no, that doesn’t happen. Your bodies don’t have enough mass to be pulled together like that.

EWWW

Joan But the earth’s gravitational pull is strong because it has so much mass. The greater the mass of the object, the greater the force of gravity.

Astronauts could bounce easily on the moon because the moon’s gravity is less than the earth’s because the moon has less mass than the earth.

Does that mean I weigh a different amount on different planets?

Joan: Well on earth, suppose you weigh 100 pounds. If you were on the moon you’d weigh about 17 pounds. But if you were on a bigger planet – say Jupiter – you’d weigh more than a whopping 236 pounds. And gravity’s effect depends upon how close objects are to one another. The earth’s gravitational pull on say, Pluto, isn’t very strong because Pluto is so far away. But the Earth’s gravitational pull on the moon is great. The Earth’s gravity keeps the moon in orbit.

So if earth’s gravity is so strong, how do astronauts get into space and why do they just float there?

Joan: Astronauts can take off from earth because the power of the rockets used to push the space shuttle out of Earth’s atmosphere, but space shuttle astronauts never travel beyond Earth’s gravitational pull, they just keep moving fast enough to keep gravity from pulling them back to Earth. It is called a state of weightlessness or as NASA calls it, micro gravity.

These Boise State University engineering students are flying in a special airplane that can create moments of weightlessness.

They’re studying the effects of micro gravity on the traction of different wheel tread designs on lunar soil and they’re also testing ways to find out how much water there is in the soil on the moon or other planets.

So gravity is one of the fundamental forces in nature. We really don’t know what causes gravity but we sure feel the effects of gravity. Whoa, you okay?

Yeah. What goes up must come down.

It’s just gravity.

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