Gravity

Gravitational field

A force field created by the mass of an object which attracts other masses placed inside of it towards the object.

Lines of force (field line)

The paths along which smaller masses follow towards a larger body.

Gravitational field strength

The force per unit mass on a small test mass placed in a gravitational field.

Radial field

Field lines are always directed towards the centre.

Uniform field

Gravitational field strength is the same in magnitude and direction throughout the field.

Gravitational potential energy (GPE)

Energy of an object due to its position in a gravitational field.

Gravitational potential

• The GPE per unit mass of an object at that point.

• The work done per unit mass to bring test mass from infinity to that point.

Why is gravitational potential always a negative value? (3)

• Potential energy of a test mass is zero at infinity from the larger mass

• To move from infinity towards the mass, the test mass must lose potential energy

• Therefore at distances below infinity, gravitational potential is negative

Equipotential

Surfaces of constant potential that require no work to move along.

Potential gradient

The change of potential per metre at that point.

Escape velocity

The minimum velocity an object must be given to escape from a planet when projected vertically from the surface

Escape velocity formula

v = √2gR

Potential difference

The work done per unit mass to move an object between two points in a gravitational field