Gravitational fields

Question 1

force field

Answer 1

a force field is a region in which a body experiences a non-contact force

Question 2

point mass

Answer 2

a mass with negligable volume or a uniform sphere whose mass acts as if its concerntrated at the centre

Question 3

force equation

Answer 3

F = Gmm / r^2

Question 4

gravitational constant

Answer 4

6.67 x 10^-11 Nm^2kg^-2

Question 5

force on masses

Answer 5

the force on m1 due to m2 is equal and opposite to the force on m2 due to m1

Question 6

the law of gravitation
inverse square law

Answer 6

F directly proportional to 1/r^2

Question 7

gravitational field strength

Answer 7

force per unit mass
vector
force always pointing towards the centre of mass

Question 8

gravitational field strength equation

Answer 8

g = F / m

Question 9

equation for g using G

Answer 9

g = GM / r^2

Question 10

g-r graph

Answer 10

1/x^2
area under = change in gravitational potential

Question 11

gravitational potential energy

Answer 11

energy stored by an object due to its position in a gravitational field
equals work done moving an object from infinity to that position

Question 12

gravitational potential

Answer 12

the gravitational potential energy that a unit mass would have at a specific point

Question 13

equation for gravitation potential

Answer 13

V = -GM / r

Question 14

value of gravitational potential at the surface of the mass and at infinity

Answer 14

surface = negative
infinity = 0

Question 15

V-r graph

Answer 15

-1/x^2
gradient = field strength

Question 16

gravitational field strength gradient

Answer 16

g = -V/r

Question 17

gravitational potential difference

Answer 17

energy needed to move a unit mass from two points at different distances from a mass have different potentials
means there is a difference in potential

Question 18

work done

Answer 18

when you move an object you do work against gravity
W = mV

Question 19

Ep equationS

Answer 19

Change in Ep = m change in V
Ep = - GMm / r

Question 20

equipotentials

Answer 20

lines (2D) and surfaces (3D) that join together a;ll points with the same gravitational potential
means if you travel along the equipotential your potential doesnt change and you dont lose or gain any energy
therefore gravitational potential difference and change in work done is both zero

Question 21

satellites

Answer 21

any smaller mass that orbits a much larger mass and kept in orbit by gravitational forces
kept in orbit by centripetal forces

Question 22

orbital speed

Answer 22

v = root(GM / r)
v directly proportional to 1 / root( r )

Question 23

equation for time period

Answer 23

T^2 = 4pi^2 / GM X r^3

Question 24

Ke and Ep of satellites
circular orbit

Answer 24

total energy is constant
in circular orbit orbital speed and distance above mass is constant
means Ke and Ep is constant

Question 25

Ke and Ep of satellites
elliptical orbit

Answer 25

the satellite will speed up as its orbital radius deacreases meaning Ke increases and Ep decreases

Question 26

escape velocity

Answer 26

minimum speed an unpowered object needs in order to leave the gravitational fields and not fall back towards the planet due to gravitational attraction

Question 27

deriving escape velocity equation

Answer 27

Ke lost = Ep gained
0.5mv^2 = GMm / r
v = root (2GM / r )

Question 28

synmchronus orbit

Answer 28

when an orbiting onject has an orbital period equal to the rotational period of the object its orbiting
e.g. geostationary satellite

Question 29

geostationary satellites

Answer 29

always above same point on earth
must in the plane of the equator
travels at same angular speedas the earth turns in the same direction ( west to east)
orbit take roughly 24h and orbital radius is 42000km, 36000km above earth

Question 30

geostationary satellites uses

Answer 30

useful for sending TV and telephone signals

Question 31

low orbiting satellites

Answer 31

satellites that orbit 180 to 2000km above earth
proximity to earth means they have high orbital speeds in comparison to earth meaning you need multiple satellites working together for constant coverage

Question 32

benefits of low orbiting satellites

Answer 32

cheaper to launch and require less powerful transmitters as they’re closer
useful for communications

Question 33

low orbiting satellite uses

Answer 33

imaging and monitoring weather