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Course: Middle school physics>Unit 2

Lesson 1: Gravitational forces

Gravitational forces

Gravity is more than just things falling down. It's an attractive force that exists between any two objects with mass. Every object with mass, like Earth or a lamp, has a gravitational pull. The strength of this pull depends on the mass of the objects and the distance between them. Even the moon feels Earth's gravity, which is why it orbits us. Created by Khan Academy.

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• I must be really strong to be able to pick up a glass of water and overpowering the whole mass of Earth, right guys?
• So your telling me, The earth is strong enough to keep a giant Space Ball floating in the sky, Yet it can't stop me from jumping? Hmmmmmmm...... Suspicious...
(1 vote)
• Why does gravitational force exist?
• You probably already know that gravity is an attractive force between objects with mass. When you reach higher levels of physics, you'll learn that gravity works by bending spacetime. But neither of those explain why gravity exists.

Gravity is one of the four fundamental forces of nature. Because gravity is foundational to how the universe works, asking why gravity exists is akin to asking why the universe exists. It's much easier for scientists to define what gravity is and explain how it works than it is to answer why it exists. In other words, we still don't know.
• why does the moon have effect on the water on the earth , why does not the moon have effect on other things? why water ?
• the gravity of the moon affects everything on earth. The water (and the air) can move more easily relative to each other and tides result. Later on you if you continue with physics you will learn that tidal forces result from the non-uniform nature of the gravitation of the moon (i.e. the water nearer the moon is pulled more strongly than the earth under it and that is pulled more strongly then the water on the far side. All of this causes a tendency to separate and results in tides.
• no way
• yes way
• Thats’ right guys we’re stronger than Earth.
• Since everybody has a gravitational pull...
does that mean the fatter you are the more gravitational pull you have?
• Yes.
F=(m₁·m₂)g/d²
F is force of gravity,m is mass,g is a constant,d is distance.
if m increases, F also increase.
• If I was in space, how big of a particle would stick me?
• in space, dust particles can orbit around astronauts because of their weak but very small gravitational force. gravity is a very strange and complex topic!:)
• Why is it that the Earth's gravitational force does not affect the tides but the moon's gravitational force does? Doesn't the earth have more mass so it would effect the tides?
• The earth's force does affect it. If not it would float off into space. It just does not vary in strength. The moon gets closer to your location than travels off to a different one. It is being pushed stronger he closer it gets.