A2 Unit 13 Gravitational Fields

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Define gravity

The universal attractive force that acts between all matter

Define a point mass

An object which behaves as if all its mass is concentrated on its centre. For a point outside a uniform sphere, the mass may be considered a point mass

Newton’s Law of Gravitation

The attractive force between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their separation

Newton’s Law of Universal Gravitation for 2 Point Masses

𝐹 = 𝐺𝑚1𝑚2 / 𝑟²

Define field strength

The force per unit mass at a point

Give the field strength for a radial gravitational field at a distance from a point mass

g = 𝐺M/r²

Define the gravitational potential at a point in a gravitational field

Work done per unit mass to move a small object from infinity to that point

Give the equation for the gravitational potential at a point in a radial field

ϕ = -𝐺M/r

Give the equation for the gravitational potential energy of a mass in a gravitational field

E_P = -𝐺Mm/r

Give the equation for the linear speed of an object orbiting a mass

v² = 𝐺M/r

What is a geostationary orbit?

A satellite which stays 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