Physics A2 · Gravitational fields. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A gravitational field is a region of space where a mass experiences a force. It is one example of a field of force. Every mass creates such a field around itself, and the force it gives is always attractive.
The gravitational field strength g at a point is the force per unit mass on a small test mass placed there. It is a vector, in the direction of the force on the mass.
Fields are drawn with field lines. The arrows show the direction of the force on a mass. Where the lines are closer together the field is stronger. Around a planet the lines are radial and point inwards. Near the surface, over a small region, they are parallel and equally spaced: a uniform field.
Students mix up field strength (force per unit mass, N kg−1) with potential (work done per unit mass, J kg−1). Read the definition for the words 'force' or 'work done'.
Answer: About 620 N.
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