Gravitational fields

You will be able to

• Use GMm / r² = mv² / r = mrω² to calculate the speed and period of a circular orbit.
• Show that T² is proportional to r³ for circular orbits and determine GM from a graph of T² against r³.
• State and explain the conditions for a geostationary orbit: period 24 h, equatorial, west to east, radius about 4.2 × 10⁷ m.

You will be able to

• Calculate the gravitational field strength g = GM / r² and the gravitational potential φ = −GM / r of a point mass.
• Explain why gravitational potential is negative and rises to zero at infinity, and calculate work done as m(φ₂ − φ₁).
• Determine the neutral point between two masses and the escape speed √(2GM / r).