C18 (Gravitational Fields) Flashcards

1
Q

Gravity

A

Universal attraction between any two masses
(Relatively weak force, only noticeable when one of masses very large, but also present tiny scale)

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2
Q

What is the gravitational pull excreted on a n object directly proportional to?

A

The mass

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3
Q

Weight

A

Force due to gravity

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4
Q

Gravitational force (equation)

A

Fg=W

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5
Q

Gravitational Field

A

Vol that gravity will act in

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6
Q

Gravitational field strengths equal to what:

A

Gravity
W=mg

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7
Q

Gravitational potential energy

A

Change GPE= mg x change h

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8
Q

‘G’-Universal

A

Same throughout universe
G, very small, only significant when at least on mass is very large

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9
Q

Why does the gravity equation contain a negative sign?

A

Indicates that force is attractive

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10
Q

What does the lines in the gravitational field indicate?

A

Direction of Fgrav would act on test mass

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11
Q

Test mass

A

Mass, small enough to not have no affect on shape of field with its own gravity

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12
Q

The more lines per area (gravitational field):

A

The stronger the field

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13
Q

How can you detect very small changes in gravity

A

Gravimeter
Used map tunnels, caves, change volcanic activity and minerals for mining

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14
Q

For object moving in a circle, what’s it’s resultant force called

A

The centripetal force

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15
Q

Centripetal force provided by…

A

Gravitational attraction of M (large body)

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16
Q

Centripetal force is equal to…

A

Gravitational force
Fc=Fg

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17
Q

Kepler’s first law

A

The orbit of every planet is an ellipse with the sun at one of the foci.

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18
Q

Perihelion

A

Closet distance to sun

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19
Q

Aphelion

A

Furthest distance from sun

20
Q

Eccentricity

A

Measure of how elongated the circle is (usually orbits have low eccentricity).

21
Q

Kepler’s second law

A

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time

22
Q

As planets move on their elliptical orbit their speed….

A

Isn’t constant
When closer they travel faster

23
Q

Kepler’s third law

A

The square of the orbital period (T) of a planet is directly proportional to the cube of its average distance (r) from the Sun

24
Q

The gradient of a graph with T squared against r cubed is…

A

4Pi^2 / GM

25
Satellite
Body that circles round another body in space
26
Give examples of natural satellites
Moons Stars Comets Asteroids Planets
27
Uses of satellites
Communication (satellite phones, not mobile phones, TV, some types of satellite radio) Military (reconnaissance) Scientific research (Study universe and monitor Earth, population crops vegetation) Weather and Climate: (Predicting and monitoring weather across the globe and monitoring long term changes in climate) Global positioning
28
Stallites orbiting Earth obey what laws
Kepler's laws
29
What provides the centripetal force on each satellite
Gravitational force between it and the Earth
30
Why don't the satellites fall towards earth if the only force acting upon them is Fg
Always falling,however travels great distance, that as it falls Earth curves away beneath it, keeping it the same height.
31
What is required for a stable orbit
Exactly right height and speed
32
The correct speed for stable orbit at distance r from centre mass of Earth is given by...
V=✓Gm/r
33
What does every satellite that is placed in a given orbit at a given height have in common
They all travel at the same speed (even if their masses vary)
34
Once launched they're normally above atmosphere, where there's no air resistance meaning...
No air resistance to slow them down, as a result they travel at a constant speed
35
Polar orbits
Circle poles Offers complete view Earth, over given period, as Earth rotates beneath, satellites covers all parts globe after number of orbits, useful for mapping and reconnaissance
36
Low Orbit
Satellites in orbit close to Earth, Kepler's third law (T squared directly proportional to r cubed) Only short time taken to orbit Earth
37
Geostationary satellites
Placed in orbit above equator As height increases T increases = can choose it's T by altering height Geostationary placed in specific orbit, so remains above same point of Earth whilst it rotates
38
To be in a geostationary orbit satellite must...
Be in orbit above Equator Rotate same direction as Earth Have orbital period, 24hrs
39
The orbital period of geostationary satellites is how long?
24hrs
40
Gravitational potential (definition):
The potential energy per kg, at any in the field. 0 potential is defined at infinity, so point close to a mass , potential of any object would be -ve.
41
Gravitational potential energy (definition):
The work done per unit mass in moving object from infinity to a point in the field.
42
Escape velocity (definition), and where is the equation derived from?
Min V required to escape gravitational field strength of an object (when projected vertically from the surface). Derived by equation 1/2 mv^2 = GMm / r
43
Fc = Fg If Fc = mv^2 / r And Fg = -GMm / r^2 Then what can be stated?
m = rv^2 / G
44
What’s the equation for V (stable velocity)?
V = square root ( GM / r )
45
Equation for change in Grav potential energy;
Change Ep = m x g x change h
46
How do you prove the T^2 is directly proportional to r^3
T=d / v T= 2pi x r / v T^2 = 4pi^2 x r^2 / v^2 v^2 = MG / r T^2 = 4pi^2 x r^3 / MG