3.7.2 Gravitational Fields

Question 1

what is gravity

Answer 1

a universal attractive force acting between all matter

Question 2

what does the gravitational force depend on

Answer 2

the mass of the two objects and the distance between them

Question 3

what is gravitational force (equation)

Answer 3

F = G m1 m2 / r2

Question 4

what is gravitational fields represented by

Answer 4

field lines

Question 5

what is gravitational field strength, g , the same as

Answer 5

acceleration due to gravity

Question 6

what is gravitational field strength

Answer 6

gravitational force on the object / mass of the object

Question 7

what is gravitational potential energy

Answer 7

GPE = the energy an object has when lifted off the ground

Question 8

what is the GPE outside the earth’s surface

Answer 8

the energy an object possesses due to its position in a gravitational field

Question 9

what is gravitational potential at a point

Answer 9

the gravitational potential energy per unit mass at that point

Question 10

what is gravitational potential

Answer 10

the work done per unit mass in bringing a test mass from infinity to a defined point

Question 11

what is the zero value of gravitational potentials

Answer 11

an infinite distance away from the mass generating that field

Question 12

what happens if an object moves along an equipotential surface

Answer 12

the potential has not changed and no work has been done on the object

Question 13

why is gravitational potential shown with a negative sign

Answer 13

the gravitational potential is trying to do the opposite of what gravity wants

Question 14

what is an orbital period

Answer 14

the time taken for an object to do one full orbit

Question 15

what is the orbital radius

Answer 15

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.

Question 16

what is the relationship between orbital period and radius (Kepler’s third law)

Answer 16

T^2 ∝ r^3

Question 17

what happens in a circular orbit

Answer 17

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

Question 18

what is escape velocity

Answer 18

the velocity needed for an object to escape a planets gravitational pull

Question 19

what happens (to energy) when an object is removed from a planets gravitational pull

Answer 19

it loses KE equal to the GPE it gains

Question 20

what is the orbital period of a geosynchronous orbit

Answer 20

one day

Question 21

what are geostationary orbits

Answer 21

appear stationary above the equator

Question 22

what are the requirements for a geostationary orbit

Answer 22

circle earth above the equator
zero eccentricity (zero deviance form orbit)
zero inclination (zero change in angle between the planes)
west-east
same rate as earth

Question 23

what are the uses of geostationary orbits

Answer 23

meteorological
communication

Question 24

why are geostationary orbits used for satellites

Answer 24

satellites view the earth from the same perspective and can provide global coverage

Question 25

what are polar orbits

Answer 25

a low earth orbit that pass above or near the earths poles and has a high inclination angle

Question 26

what are the requirements for a polar orbit

Answer 26

low altitudes (200-1000km)
north-south
orbit time about 100 mins
inclination about 90 degrees to equator
speed about 7.5 km/s

Question 27

what are the uses of polar orbits

Answer 27

earth observation

Question 28

why are polar orbit satellites used

Answer 28

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