An object will experience a force when put in a gravitational field. The force is always attractive: F=-GmM / r^2

You can draw gravitational field lines around a mass. Since gravity is attractive, the direction is always towards to centre of the mass.

The field strength is the force per unit mass. It can be worked out using g = F/m or the equation g=-GM/ r^2. In can also be called the acceleration due to gravity.

The force in a uniform gravitational field can be calculated using F=mg

Gravitational potential energy is equal to mgh in a uniform field or E = -GMm /r in a non uniform field. It is the work which would need to be done to move a mass against the force of gravity. Potential energy is zero at infinity and negative on the earths surface.

The gravitational potential is the potential energy per unit mass V = E /m or V=-GM/r. Equipotentials in a diagram shows all the points in a field which have the same potential. No work is done moving across them.

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