Gravitational fields

What you'll learn

• Understand that a gravitational field is an example of a field of force and define gravitational field as force per unit mass.
• Represent a gravitational field by means of field lines.
• Recall and use Newton’s law of gravitation F = Gm1m2/r2 for the force between two point masses.
• Analyse circular orbits in gravitational fields by relating the gravitational force to the centripetal acceleration it causes.
• Understand that a satellite in a geostationary orbit remains at the same point above the Earth’s surface, with an orbital period of 24 hours, orbiting from west to east, directly above the Equator.
• Derive, from Newton’s law of gravitation and the definition of gravitational field, the equation g = GM/r2 for the gravitational field strength of a point mass.
• Define gravitational potential at a point as the work done per unit mass in bringing a small test mass from infinity to the point.
• Use Φ = −GM/r for the gravitational potential in the field due to a point mass and Ep = −GMm/r for gravitational potential energy.

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