5.4: Gravitational Fields, F Flashcards Preview

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Flashcards in 5.4: Gravitational Fields, F Deck (25)
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1
Q

Define: gravitational field

A

Region around a body in which other bodies around it experiences a non-contact force due to the mass of the body

2
Q

Define: gravitational field strength

A

Any point in a gravitational field is the force acting per unit mass at that point, (g=F/m)

3
Q

The force experienced by an object is always __________

A

The force experienced by an object is always attractive

4
Q

Define: Newton’s Law of Gravitation?

A
  • Gravitational force of attraction between two masses is directly proportional to the product of their masses and inversely proportional to the square of their separation.
  • An inverse square law: F ∝1/r^2
5
Q

Explain using Newton’s law of gravitation, what would happen if you manipulated one of the variables

A

-If the distance(r) increases then the force(F) will decrease
and
-If the distance(r) doubles then the force(F) will be one quarter(1/4) the strength of the original force

6
Q

Define: Gravitational field lines

A

Lines which show the shape and direction of the force that masses would feel when placed at that point

7
Q

The Earth’s gravitational field is radial. What does it mean by that

A

The lines of force meet at the centre of the Earth

8
Q

In a ______ Field, g is _________ Proportional to r^2

A

In a radial field, g is inversely proportional to r^2

9
Q

Define: Gravitational Potential

A

Work done in moving a Unit Mass from infinity to that point

10
Q

Vg= - GM/r (Vg being gravitational potential in J/kg)

Why is Gravitational potential negative?

A

Work is done against the gravitational field to move an object out of the gravitational field.

11
Q

Explain what Gravitational Potential difference is

A

Work done moving a Unit mass. 2 points at different distances will have different gravitational potentials ∴ the difference is the amount of energy you need to move the object

12
Q

Define: Gravitational potential energy

A

Gravitational potential is work done per unit mass ∴ gravitational potential energy of an object at a point in a gravitational field is E =mVg

13
Q

Define: Escape velocity

A
  • Minimum lunch velocity required required to move an object from that point to infinity
  • (minimum energy to escape a gravitational field)
14
Q

How can you derive escape velocity?

A

By equating kinetic energy to gravitational potential energy
0.5mv^2 = GMm/r
rearrange and cancel m’s

15
Q

What is a satellite?

A

Any small mass which orbits a larger mass

e.g. moon is a satellite of earth

16
Q

What factors does the speed of an orbit rely on

A
  • Radius

- Mass of the larger body

17
Q

How can we derive the equation to find the speed of an orbit

A

By equating centripetal force with the force of gravity
F =-GMm/r^2 and F = mv^2/r

rearrange and cancel m’s to find v (orbit speed)

18
Q

How can we derive the time period for one orbit

A

By equating 2 circular motion equations and subbing in the equation for orbit velocity
v=wr and w=2π/T

19
Q

Define: Geostationary orbit

A

An orbit of the earth made by a satellite that has the same time period and orbital direction as the rotation of earth(24hrs) and is in the equatorial plane(above equator)

20
Q

What are geostationary satellites used for

A
  • Monitoring air traffic
  • Monitoring weather and changes in environment
  • TV signals and relying mobile telephone signals
21
Q

What are the downsides of using geostationary satellites

A
  • Expensive

- Small risk of something going wrong and it falling back to earth

22
Q

State Kepler’s first law

A

Planets travel around the sun in elliptical orbits

23
Q

State Kepler’s second law

A

A line joining the sun to a planets will sweep out equal areas in equal times

24
Q

Define: Kepler’s third law

A

The time period squared of a planet orbiting the sun is proportional to the mean radius of its orbit cubed, or T^2 ∝ r^3

25
Q

How can Newton’s law of gravitation be used to explain how thick a planet’s atmosphere is

A
  • A planet exerts a force all the particles, otherwise they would float off into space.
  • The larger a planet, the larger the force is further away from its surface ∴ the more atmosphere particles it can stop escaping, leading to a thicker atmosphere