Week 11 Gravitation Flashcards
what is Newton’s law of gravity
every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them
what is the general gravitational force equation
F = GMm/r^2
what can be said about the gravitational force exerted by a spherically symmetric mass
it can be treated as though all the mass were concentrated at its centre
how can we find the net gravitational force for a group of point masses
using the principle of superposition
what 2 things can be said about gravitational potential energy
> it has no definitive zero level
>it is attractive so values are negative
what is the gravitational potential energy formula
U = -GMm/r
define escape velocity
minimum velocity that an object must have in order to escape the gravitational force of another reaching rest at infinity
what is the escape velocity formula
v = sqrt (2GM/R)
how do we find the net GPE for a system of more than 2 bodies
find the individual GPE for each pair of bodies as though the others don’t exist and add them algebraically
what is the orbit velocity formula
v = sqrt (GM/R)
what is the total mechanical energy of a satellite in circular orbit
E = KE + GPE = 1/2GPE = -KE
what is the equation for total mechanical energy of a satellite in elliptical orbit
E = -GMm/2a
a is the semi major axis of orbit
what are Kepler’s 3 laws of planetary motion
1 All planets move in elliptical orbit with its star at one focus of ellipse
2 A line that connects a planet to the Sun sweeps out equal areas in equal time
3 The square of the period of any planet about the Sun is proportional to the cube of the planet’s mean distance from the Sun
what is the assumption made by Kepler’s laws and why is it wrong
assumes the star remains perfectly stationary however in reality it wobbles about its axis due to gravitational attraction to other objects in the solar system
what are ocean tides a result of
gravitational tidal forces due to a combination of Earth’s rotation about its axis and gravitational attraction of Sun and Moon
