gravitation

what does gravity act on

any object which has mass

is gravity repulsive or attractive

always attractive

Newton’s law of gravitation

the magnitude of the gravitational force between two masses is directly proportional to the product of the masses and inversely proportional to the square of the distance between their centres of mass 

gravitational field strength

the force per unit mass exerted by a gravitational field on an object

is gravitational field strength constant?

constant in uniform fields

varies in radial fields

when can the equation be used

for radial fields only 

gravitational potential

the work done per unit mass against gravitational force to move an object from infinity to a given point

gravitational potential at infinity

0

is gravitational potential positive or negative, and why?

it is always negative

as an object moves from infinity to a point energy is released as GPE is reduced

what is M in the equation

mass of the object causing the field

gravitational potential difference

energy released to move a unit mass between two points

work done when moving an object in a gravitational field, what is m

mass of the object being moved

why is no work done when moving along an equipotential surface

gravitational potential difference is 0

Kepler’s third law derivation (T² is directly proportional to r³)

completed derivation

total energy of an orbiting satellite

kinetic energy + potential energy

always constant

escape velocity

minimum velocity an object must travel at to escape the gravitational field at the surface of a mass

synchronous orbit

orbital period of the satellite is the same as the rotational period of the object it is orbiting

geostationary satellite

specific geosynchronous orbit (orbital time period = 24hrs)

stays above the same point on earth

directly above equator

use of geostationary orbits

TV + telephone signals

uses of low orbit satellites

weather monitoring, military applications