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### Gravity & Orbits

• The force of gravity is based off of the mass of the objects involved (m1,  m2), the distance between the objects (r), and the universal gravitational constant (G).
 | → F g | = G · m1 ·m2 r2 .
• The universal gravitational constant is
 G = 6.67 ·10−11  N · m2 kg2 .
• The force of gravity acts on each object equally, and the direction of the force is towards the center of the other object.
• A gravitational field is an area we can treat as having a constant acceleration. Like the surface of the Earth, in some places the force will only change a negligible amount in the area around the object's location.
• We denote a gravitational field with ag. Thus, for an object of mass m in the field, Fg = m ·ag.
• If we want to find the gravitational field for a given object with mass M at distance r, it is
 ag = G · M r2 .
• If something is in orbit, it must have a centripetal force to keep it in the orbit. Gravity provides this centripetal force. For a simple circular orbit where one object is much more massive than the second object, it follows the relation
G · m1 ·m2

r2
= m2  | → v |2

r
.

## Gravity & Orbits

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