You're watching FreeSchool!
Any time you drop something, it falls down.
But - why? Why do you come back down, no matter how hard you jump on that trampoline?
When you throw a ball, why does it fall to the ground instead of flying off into space?
The answer is gravity, but it does a lot more than pulling things down.
Gravity is an invisible force that pulls objects towards each other. In most cases,
when we say "gravity" we are talking about the earth's gravity, but anything that has mass
has gravity, too. Yes, even you have gravity! Of course, you don't have very much gravity.
The more mass something has, the more gravitational force it has.
Compared to the gravity of the earth, any gravitational force that you
have is too weak to notice. Mass is not the same as weight.
Mass is a measure of the matter in an object, and does not change no matter where you go.
On the other hand, weight measures the pull of gravity on an object, and this can change.
Most places on earth have roughly the same amount of gravity,
but if you were to leave earth, the pull of its gravity would weaken the farther away you went,
until eventually you would experience zero-g. This is because gravity gets weaker with distance.
There is still gravity in space, because everything that exists exerts gravitational force,
but the gravitational pull from something like a person or even
a spaceship is so small it feels as though you have no weight at all.
If you were to land on another planet or celestial body, the pull of gravity would
be different depending on its mass, and you would not weigh the same as you did on earth.
On the moon, for example, gravity is only about 17% of earth's.
This is because the moon is much less massive than the earth. A person who weighs 100 pounds
or 45 kilograms on earth would weigh only 17 pounds or 7 and a half kilograms on the moon.
On Mars, the same person would weigh 38 pounds or 17 kilograms.
On Jupiter they would weigh 253 pounds or 106 kilograms.
Gravity is the weakest of the four fundamental forces of the universe,
and only gets weaker with distance, but it is very important for life on Earth.
It is the force that holds us down to the surface of the planet.
Gravity makes things fall down, and gives things weight.
It is what holds the Earth together, and keeps the air we breathe from spinning off into space.
Gravity also holds our solar system together. The earth's gravity holds the moon in orbit around the
Earth. The sun's gravity holds the Earth and all the other planets in orbit around the sun.
On a larger scale, even the Milky Way galaxy is held together by gravity.
Scientists believe that a supermassive black hole sits at the center of the Milky Way,
with its gravity holding all the gas, dust, stars and systems in place around it. Black holes have
so much mass in such a small space that their gravitational pull is very strong. They generate
such strong gravity that not even light can escape from them, and that's why they look black!
So you see, while gravity may be an invisible force,
it has a very visible impact on our lives.