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Advanced concepts in gravitational fields

The term gravitational field $$\vecphy{g}$$ has quite different meanings in informal and formal scientific settings.

  • Informally, it can mean a region of space in which a gravitational force acts on a body. This is the meaning referred to when people say, for example, that there is a gravitational field around a star.

  • In scientific settings, a gravitational field is a quantity that specifies the force (both the magnitude AND direction) acting on a unit mass at a specific point in space.

The value of a field function is different for different points in the field, due to the law of universal gravitation. This reflects, for example, that the force is weaker further away from a point mass.

The format of the function depends on the shape and alignment of masses.

The magnitude of the field at a point is equal to the gravitational field strength $$g$$. In other words, the gravitational field strength is the scalar of the gravitational field.

In principle, any mass will exert a gravitational force on an object placed anywhere in space. In practice as the distance increases the force becomes infinitesimally small even for large masses.

In a uniform field the gravitational field strength and the direction of the force is the same at any point in the field.

For small distances above the surface of the earth, the gravitational field can be treated as uniform. This is because the distance from the earth's surface to the atmosphere is very small compared to the radius of the earth.