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Physics > 8 Astrophysics > Flashcards

8 Astrophysics Flashcards

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1
Q

What do planets and comets travel around?

A

They travel around the sun.

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2
Q

What do moons and satellites travel around?

A

They travel around the planets.

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3
Q

How do these things travel?

A

For this to happen, there must be forces being applied to them.

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4
Q

What did Newton say in his theory of gravity to explain these movements?

A

Newton suggested that between any two objects there is always a force of attraction.

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5
Q

What is this attraction due to?

A

This attraction is due to the masses of the objects.

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6
Q

What is this force called?

A

He called this force gravitational force.

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7
Q

What did Newton suggest that the size of this force depended on?

A

1) Masses of the two objects.
2) Distance between the masses.

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8
Q

What happens to the attractive forces as there is a greater mass of objects?

A

The greater the masses of the two objects the stronger the attractive forces between

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9
Q

What happens if the distance between the masses increase in terms of the forces between them?

A

If the distance between the masses is increased the forces between them decrease.

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10
Q

What kind of law do these gravitational forces follow?

A

If the distance between the masses is doubled, the forces between them are quartered; if the distance between them is trebled, the forces become one ninth of what they were.

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11
Q

What is the size of the gravitational attraction between objects with small masses?

A

It is tiny.

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12
Q

When is the force of attraction obvious?

A

Only when one or both of the objects has a very large mass

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13
Q

What is an example of when one or both of the objects have a large mass and the force of attraction is obvious?

A

For example, a moon or a planet - the force of attraction is obvious.

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14
Q

How big is our sun?

A

Our sun is massive.

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15
Q

How do we know that our sun is massive?

A

It contains over 99% of the mass of the Solar System.

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16
Q

Why is the sun so important to our solar system?

A

It is the gravitational attraction between this mass and each of the planets that holds the Solar System together and causes the planets to follow their curved paths.

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17
Q

What is a diagram which shows that the gravitational forces make the planets follow nearly circular paths?

A
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18
Q

Which planets feel the greatest attraction and follow the most curved paths?

A

Those planets that are closest to the Sun feel the greatest attraction and so follow the most curved paths.

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19
Q

Which planets feel the weakest pull and follow the least curved paths?

A

Planets that are the furthest from the Sun feel the weakest pull and follow the least curved path.

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20
Q

What is the order of the planets from the sun?

A

Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune

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21
Q

What is a diagram of the planets and their average distances along with the time it takes for one orbit of the sun in years?

A
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22
Q

What is the trend shown by this graph?

A

The larger the average distance, the longer the time it takes for the planet to orbit the sun in earth years.

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23
Q

What is a satellite?

A

It is an object that orbits a planet.

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24
Q

What are the two types of satellites?

A
  • Natural.
  • Artificial (man-made).
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25
Q

What are natural satellites called?

A

They are called moons.

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26
Q

How many moons does the earth has?

A

The Earth has just one moon.

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27
Q

How big is the earth’s moon?

A

It is the fifth largest moon in our Solar System.

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28
Q

How far away is the moon from earth?

A

340 000 km from earth.

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29
Q

How long does it take for the moon to complete an orbit?

A

It takes just over 27 days to complete one orbit.

30
Q

What is an orbit?

A

It is the path of a planet around a star or satellite around a planet.

31
Q

Why is it wrong to call our moon ‘The moon’?

A

This is because it is not unique. Many planets have moons.

32
Q

Do all planets have one moon?

A

No, some have more than one.

33
Q

What are some examples of planets with more than one moon?

A

Mars has two moons while Jupiter and Saturn have more than 60 each.

34
Q

What kind of orbits do moons have?

A

All moons have circular orbits.

35
Q

Why do moons have circular orbits?

A

Because of the gravitational forces between them and their planet.

36
Q

Since when have humans been able to launch, and put into orbit artificial satellites around earth?

A

Since the late 1950s.

37
Q

Why do we put these artificial satellites into orbit?

A

Because they are extremely useful.

38
Q

What are the two kind of orbits that these artificial satellites are put into?

A
  • Very high orbit.
  • Much lower orbit.
39
Q

Why are satellites put into very high orbits?

A

These satellites are used to help us communicate over large distances.

40
Q

What is an example of these satellites helping us communicate over large distances?

A

These satellites are used for international phone calls, video links, and the internet etc.

41
Q

Why are satellites put into very low orbits?

A

They are used to monitor in detail the Earth’s surface.

42
Q

What is an example of these satellites monitoring the Earth’s surface in detail?

A

They are used to observe some of the world’s oceans or the progress of forest fires.

43
Q

What are comets?

A

Comets are large rock-like pieces of ice that orbit the sun.

44
Q

What do the orbits of comets look like?

A

They have very elliptical (elongated) orbits which at times take them very close to the Sun.

45
Q

Do their orbits keep them close to the sun?

A

No, at other times they travel close to the very edge of our Solar System.

46
Q

When do comets travel fastest?

A

When they are close to the sun.

47
Q

What is an image that shows how the speed of a comet varies enormously?

A
48
Q

What is the force that causes moons to orbit planets?

A

Gravitational force.

49
Q

What is the force that causes the planets and comets to orbit the sun?

A

Gravitational force.

50
Q

What is the force that causes artificial satellites to orbit the earth?

A

Gravitational force.

51
Q

What is gravitational field strength?

A

The strength of gravity on a planet or moon.

52
Q

What letter represents gravitational field strength?

A

g.

53
Q

Do all planets have the same gravitational field strength?

A

Different planets have different masses and different radii.

54
Q

What are the two factors that affect gravitational field strength?

A
  • The mass.
  • The radius.
55
Q

How does the mass affect the gravitational field strength?

A

The larger the mass of a planet the greater its gravitational field strength.

56
Q

How does the radius affect the gravitational field strength?

A

The larger the radius of a planet the smaller the gravitational field strength at its surface.

57
Q

What is the gravitational field strength on earth?

A

It is approximately 10N/kg.

58
Q

What is the gravitational field strength on the moon?

A

It is approximately 1.6N/kg.

59
Q

Why does our weight change on different planets?

A

Our weight depends on gravitational field strength since W=mass x g. The Gravitational field strength of a planet varies with its mass and radius so depending on the mass and radius of the different planet, our weight changes.

60
Q

What is a table that shows the relationships between the diameter, mass and gravitational field strengths?

A
61
Q

What is the relationship between the gravitational field strength on the moon and earth.

A

On the moon, the gravitational field strength is only one sixth that of the Earth’s

62
Q

What does this difference of 1/6 mean in terms of our weight?

A

This means that on the moon you would weigh six times less.

63
Q

What is a diagram which shows how there is a difference in one person’s weight on the moon and on Jupiter?

A
64
Q

What is the orbital speed?

A

The speeds of objects as they circle other objects, for example, the moon going around the earth.

65
Q

How do the orbital speeds of satellites vary?

A

They vary greatly depending on the tasks they are performing.

66
Q

How can we tell that the orbital speeds vary greatly?

A
  • Communication satellites (high orbits) travel at approximately 3km/s.
  • Observation satellites (low polar orbits) travel at approximately 8km/s.
67
Q

How can we calculate the orbital speed?

A

Orbital speed = 2 x pi x r
————
T

68
Q

What is r in this equation?

A

Orbital radius (circumference of the circular orbit, r)
SEE EXAMPLE ON PAGE 264.

69
Q

What is T in this equation?

A

Time for one complete orbit.

70
Q

What can we use this equation to calculate?

A
  • Speed of satellites.
  • Speed of planets.
71
Q

When calculating the speeds of planets, what is r?

A

It is the average distance from the sun.

Physics (24 decks)

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