Gravity

=__//**Newton's Law of Universal Gravitation **//__=







__Gravity Inside the Earth__


Upon entering the earth, the radius between you and the center decreases, so the gravitational force increases (represented by A). However, once you pass the outer shells of mass of the earth, the majority of the mass is outside of the radius you have reached, so gravity pulls you back outward (represented by B). At the center of the earth all the forces cancel each other out and the force of gravity = 0.



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__Geosynchronous Orbits__
An orbit is considered geosynchronous when the same face of the satellite is constantly facing the same point on Earth. Examples would include cell phone satellites (and all forms of communications) and satellite television.

=Gravitational Potential Energy and Escape Velocity= The general expression for gravitational potential energy arises from the law of gravity and is equal to the work done against gravity to bring a mass to a given point in space. Because of the inverse square nature of the gravity force, the force approaches zero for large distances, and it makes sense to choose the zero of gravitational potential energy at an infinite distance away. The gravitational potential energy near a planet is then negative, since gravity does positive work as the mass approaches. This negative potential is indicative of a "bound state"; once a mass is near a large body, it is trapped until something can provide enough energy to allow it to escape. The general form of the gravitational potential energy of mass m is:

where G is the gravitation constant, M is the mass of the attracting body, and r is the distance between their centers.

This is the form for the gravitational potential energy which is most useful for calculating the escape velocity from the earth's gravity.