Gravitational Fields

Definition of gravitational potential, V?

The work done per unit mass to move a small object from infinity to that point

What is the definition of a gravitational field?

the region surrounding an object in which it exerts a gravitational force on any other object.

A small mass placed in Earth's gravitational field will be?

1) Attracted towards the Earth 2) will have its own gravitational field that does not have a noticeable effect on the earth because earth is so massive

How do geosynchronous satellites work?

1) Geosynchronous satellites orbit directly over the equator and are always above the same point on Earth. 2) A Geosynchronous satellite travels at the same angular speed as Earth. 3) This type of satellite is useful for sending TV and telephone signals - the satellite is relative to a point on Earth, so you don't have to alter the angle of your receiver. (or transmitter) 4) Their orbit takes exactly 24 hours.

How is the energy of an orbiting satellite constant?

1) In a circular orbit, the satellites speed and distance above the mass it's orbiting is kept constant. This means its kinetic energy and potential energy are both constant. 2) In a elliptic orbit, a satellite will speed up as it's height decreases. This means kinetic energy increases as potential energy decreases (vice versa) so the total energy remains constant.

Graph of gravitational potential against r shows?

1) V is negative at the surface of a mass and increases with distance 2) The gradient of this graph at a particular point is g g=-ΔV/Δr

What does the graph of g against r show?

1) g is greatest at the surface of the earth 2) g decreases rapidly as you move away from earth 3) The area under this graph gives Gravitational Potential, V

What will masses in a gravitational field experience?

A force of attraction.

What is the definition of a gravitational field line?

A line followed by a small mass in a gravitational field, acted on by no other forces than the force due to the field.

What is an equipotential line?

A line in a gravitational field along which the gravitational potential is constant.

What is the definition of a gravitational force?

An attractive force that acts equally on any two objects due to their mass.

Why can we assume that at the Earth's surface g is constant?

At the earth's surface the gravitational field of the earth is (almost) uniform

Newton's law of gravitation?

The gravitational force F between two point masses m₁ and m₂ at distance r apart is F=GMm/r²

What is the shape of Earth's gravitational field?

It is radial, the lines of force meet at the centre of the earth

What does Newton's law of gravitation assume?

That the gravitational force between two points is: 1) Always an attractive force 2) Proportional to the mass of each object 3) Proportional to the inverse square distance between the two points

What is the Gravitational potential difference?

The difference in potential between two points

Close to the Earth's surface, what happens to the field?

The field is (almost) uniform the field lines are almost (almost) parallel

What is the gravitational field strength (g)?

The force per unit mass on a small mass placed in the field F=mg or g=F/m in NKg⁻¹

What is F proportional to?

The inverse square of distance? It follows the inverse square law.

What is G?

The universal gravitational constant is the constant of proportionality.

Equation for Gravitational potential?

V = -GM/r

When will an object with a mass experience an attractive force?

When it is put in the gravitational field of another object.

What happens when you move an object?

Work is done on the field - the amount of energy you need depends on the mass of the object and the gravitational potential difference ΔW=mΔV W - work done in J V - gravitational potential difference in JKg⁻¹

How are Planets and Satellites kept in Orbit?

by the gravitational field 'pull' of the object they're orbiting

Is g vector or scalar?

g, is a vector quantity that is always pointing towards the centre of mass whose field you're describing

What is acceleration due to gravity?

g, is the acceleration of a mass in a gravitational field

In a radial field what is g inversely proportional to?

r² g=GM/r² (M is the point mass)

At infinite distance from a mass what will the gravitational potential be?

zero