3.7.2 Gravitational Fields Flashcards
what is gravity
a universal attractive force acting between all matter
what does the gravitational force depend on
the mass of the two objects and the distance between them
what is gravitational force (equation)
F = G m1 m2 / r2
what is gravitational fields represented by
field lines
what is gravitational field strength, g , the same as
acceleration due to gravity
what is gravitational field strength
gravitational force on the object / mass of the object
what is gravitational potential energy
GPE = the energy an object has when lifted off the ground
what is the GPE outside the earth’s surface
the energy an object possesses due to its position in a gravitational field
what is gravitational potential at a point
the gravitational potential energy per unit mass at that point
what is gravitational potential
the work done per unit mass in bringing a test mass from infinity to a defined point
what/where is the zero value of gravitational potentials
an infinite distance away from the mass generating that field
what happens if an object moves along an equipotential surface
the potential has not changed and no work has been done on the object
why is gravitational potential shown with a negative sign
the gravitational potential is trying to do the opposite of what gravity wants
what is an orbital period
the time taken for an object to do one full orbit
what is the orbital radius
the average distance between the centre of the body and the centre of the object, for a circle this is constant, but changes for an elliptical orbit.
what is the relationship between orbital period and radius (Kepler’s third law)
T^2 ∝ r^3
what happens in a circular orbit
in a circular orbit around a planet, the satellite is always on the same equipotential and so the total energy of an orbiting satellite is constant
what is escape velocity
the velocity needed for an object to escape a planets gravitational pull
what happens (to energy) when an object is removed from a planets gravitational pull
it loses KE equal to the GPE it gains
what is the orbital period of a geosynchronous orbit
one day
what are geostationary orbits
appear stationary above the equator
what are the requirements for a geostationary orbit
circle earth above the equator
zero eccentricity (zero deviance from orbit)
zero inclination (zero change in angle between the planes)
west-east
same rate as earth
what are the uses of geostationary orbits
meteorological
communication
why are geostationary orbits used for satellites
satellites view the earth from the same perspective and can provide global coverage
what are polar orbits
a low earth orbit that pass above or near the earths poles and has a high inclination angle
what are the requirements for a polar orbit
low altitudes (200-1000km)
north-south
orbit time about 100 mins
inclination about 90 degrees to equator
speed about 7.5 km/s
what are the uses of polar orbits
earth observation
why are polar orbit satellites used
satellites can view entire earth’s surface multiples times a day
allows scientific research to study earth’s atmosphere, oceans and land cover
natural disasters can be monitored and the collection of long term data
