18.1 - 18.7 Flashcards
whats a gravitational field
a field created around an object with mass. it has infinite range but the strength is negligible at long distances
define ‘gravitational field strength’
the gravitational force exerted per unit mass on an object placed within a gravitational field
state Newtons law of gravitation
the force between two point masses is directly proportional to the product of the masses and inversely proportional to the distance between them squared
why is there a negative sign in the equation for Newtons law of gravitation
to show its an attractive force
Kepler’s first law
the orbit of a planet is an ellipse with the sun at one of the two foci
Kepler’s second law
a line segment connecting a planet to the sun sweeps out equal areas during equal intervals of time
Kepler’s third law
the square of the orbital period of a planet is directly proportional to the cube of its average distance from the sun
define ‘aphelion’ and ‘perihelion’
aphelion: furthest point from the sun in an orbit
perihelion: closest point to the sun in an orbit
define ‘astronomical unit’
the mean distance from the earth to the sun
uses of satellites
communication
reconnaissance for the military
scientific research
monitoring weather
what’s a geostationary orbit
when the orbit of a satellite leaves it in the same position relative to a point on earth by orbiting the equator at the same speed as earth’s rotation
define ‘gravitational potential’
the work done per unit mass to bring an object from infinity to a point in a gravitational field. measured in J/kg
define ‘escape velocity’
the minimum velocity at which an object has enough energy to leave a specified gravitational field
derive Kepler’s third law
a=ω^2 *r = (2π/T)^2 *r
g=GM/(r^2)
GM/(r^2) =4π^2/T^2 *r
T^2 = (4π^2)/GM *r^3
how do you determine the escape velocity?
gravitational potential * mass = kinetic energy required
