Gravitational Field (College Board AP® Physics 1: Algebra-Based)

Gravitational field

• A field models the effects of a noncontact force exerted on an object at various positions in space

  • A noncontact force is a force that occurs between objects or systems without them touching each other

• A gravitational field is defined as:

A region of space where a mass experiences a force due to the gravitational attraction of another mass

• The force experienced by a mass is called the gravitational force, the direction of these forces can be shown using vectors

  • The direction of the vector shows the direction of the gravitational force that would be exerted on a mass if it was placed at that position in the field

  • These vectors are known as field lines (or 'lines of force')

• Gravitational fields are always directed toward the center of the largest mass

  • This is because gravitational forces are attractive only (they are never repulsive)

  • Therefore, masses always attract each other via the gravitational force

Representing gravitational fields

• The direction of a gravitational field is represented by gravitational field lines 

  • Therefore, gravitational field lines also show the direction of acceleration of a point mass placed in a field

• The strength of a gravitational field is represented by the density of the gravitational field lines

  • The closer the field lines then the stronger the gravitational field

  • An object with a larger mass will have a stronger gravitational field

  • For example, the gravitational field strength of the Moon is less than the Earth

Non-uniform gravitational field

• The gravitational field around a point mass will be radial in shape and the field lines will always point towards the centre of mass

  • For example, an object far away from the surface of the Earth in space experiences a gravitational force due to the radial field lines around the Earth

• Radial fields are considered non-uniform fields

  • The gravitational field strength is different depending on how far you are from the center of the point mass

Object in a radial gravitational field

Uniform gravitational field

• The gravitational field lines of a uniform field, where the field strength is the same at all points, is represented by equally spaced parallel lines

  • No matter how far away an object is from the center of mass but still within the uniform field, the gravitational field strength is the same

• For example, an object on or near the Earth's surface experiences a gravitational force due to the Earth's uniform gravitational field where

Gravitational field lines