Gravitational fields

gravitational field strength

Force per unit mass in a gravitational field (in the uniform field close to earth, it is numerically equal to the acceleration of freefall)

Newton's law of gravitation

Force between two point masses is proportional to the product of the masses and inversely proportional to the square of the distance between them

Kepler's First Law

The orbit of a planet is an ellipse with the Sun at one of the two foci.

Kepler's Second Law

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

Kepler's Third Law

The square of the orbital period T of a planet is directly proportional to the cube of its average distance r from the Sun.

geostationary orbit

A satellite placed in a geostationary orbit remains above the same point on the Earth while the Earth rotates. In order to be in a geostationary orbit, the satellite must:

• Be in an orbit above the Earth's equator

• Orbit in the same direction as the Earth's rotation

• Have an orbital period of 24 hours

gravitational potential at a point

The work done per unit mass to move an object to that point from infinity

gravitational potential energy at a point

The gravitational potential energy E of any object with mass m within a gravitational field is the work done to move the mass from infinity to a point in a gravitational field

escape velocity

The minimum velocity required for an object to have just enough kinetic energy to leave the gravitational field