Gravitational fields Flashcards

1
Q

force field

A

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

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2
Q

point mass

A

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

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3
Q

force equation

A

F = Gmm / r^2

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4
Q

gravitational constant

A

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

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5
Q

force on masses

A

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

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6
Q

the law of gravitation
inverse square law

A

F directly proportional to 1/r^2

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7
Q

gravitational field strength

A

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

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8
Q

gravitational field strength equation

A

g = F / m

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9
Q

equation for g using G

A

g = GM / r^2

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10
Q

g-r graph

A

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

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11
Q

gravitational potential energy

A

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

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12
Q

gravitational potential

A

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

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13
Q

equation for gravitation potential

A

V = -GM / r

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14
Q

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

A

surface = negative
infinity = 0

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15
Q

V-r graph

A

-1/x^2
gradient = field strength

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16
Q

gravitational field strength gradient

17
Q

gravitational potential difference

A

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

18
Q

work done

A

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

19
Q

Ep equationS

A

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

20
Q

equipotentials

A

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

21
Q

satellites

A

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

22
Q

orbital speed

A

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

23
Q

equation for time period

A

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

24
Q

Ke and Ep of satellites
circular orbit

A

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

25
Ke and Ep of satellites elliptical orbit
the satellite will speed up as its orbital radius deacreases meaning Ke increases and Ep decreases
26
escape velocity
minimum speed an unpowered object needs in order to leave the gravitational fields and not fall back towards the planet due to gravitational attraction
27
deriving escape velocity equation
Ke lost = Ep gained 0.5mv^2 = GMm / r v = root (2GM / r )
28
synmchronus orbit
when an orbiting onject has an orbital period equal to the rotational period of the object its orbiting e.g. geostationary satellite
29
geostationary satellites
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
30
geostationary satellites uses
useful for sending TV and telephone signals
31
low orbiting satellites
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
32
benefits of low orbiting satellites
cheaper to launch and require less powerful transmitters as they're closer useful for communications
33
low orbiting satellite uses
imaging and monitoring weather