gravitational fields

• no work is done when moving an object along a line of equipotential
• potential difference is the difference in potential in 2 points of a gravitational field
• gravitational potential energy is the work done on the system to move a mass from infinity to its current position
• GPE is 0 at infinity and the only work done to bring it to its position is the attractive force of gravity so the work done on the system will be negative
• potential is the potential energy per unit mass
• the potential gradient is the gradient of the potential/distance graph
• the potential gradient is equal to gravitational field strength
• change in potential is the area under a gravitational field strength/distance graph
• Kepler's law of orbits is $T^2=$$kr^3$
• $T^2=$$\frac{4\pi^2r^3}{GM}$ = time period of object in orbit
• total energy of orbit = kinetic energy store + gravitational potential energy store
• total energy must stay constant so each energy store changes to compensate
• escape velocity is the minimum speed required to leave a gravitational field
• escape velocity = $\sqrt{\frac{2GM}{r}}$
• escape velocity does not depend on mass of object
• value of escape velocity is always higher than orbital velocity
• synchronous orbit = objects orbiting period is the same as the rotational period of what it is orbitting
• geosynchronous orbit is a synchronous orbit above earth
• geosynchronous orbits must be above the equator
• low orbiting satellites orbit between 180 and 200 km above earth's surface
• low orbiting satellites have a faster period so can be used for monitoring conditions
• geosynchronous satellites are used for communication as they are easily located
• gravitational field strength is the force per unit mass experienced by an object in a gravitational field
• a field line is the path taken by a small test mass