Gravitational fields Flashcards
What is a force field?
A region where objects experience a non-contact force
What is gravity?
It is a universal attractive force between all matter
How can force fields be represented?
They can be represented as vectors, showing the direction of the force they would exert on an object placed in that field.
What are gravitational field lines?
They are arrows showing the direction of the forces that masses would feel in a gravitational field.
What is the Earth’s gravitational field like?
It is a radial gravitational field- the lines of force meet at the centre of the Earth
What happens to the force experienced by a mass,m, as it moves further away from the Earth?
The lines of force are further apart and the force experienced decreases
What is the Earth’s gravitational field like close to the Earth’s surface?
It is almost uniform and the field lines are almost parallel and equally spaced
State Newton’s Law of Gravitation
The force between two masses is directly proportional to the product of their masses and inversely proportional to the square of their distance apart
What is gravitational field strength(g)?
The force per unit mass on a small test mass placed in the field
What type of quantity is g?
It is a vector, always pointing towards the centre of the larger mass
What is gravitational potential energy?
It is the energy of an object due to its position in a gravitational field(J)
What is gravitational potential?
It is the work done per unit mass to move a small object from infinity to that point(potential energy per unit mass)
(J/kg)
Why is gravitational potential negative?
It is negative because you have to do work against the gravitational field to move an object out of it.
This means that at an infinite distance from the large mass, the potential will be zero.
Therefore, the potential energy becomes less negative as the object moves further upwards.
What is the gravitational potential gradient?
The change of potential per metre at that point(J/kg/m)
What is the gradient of a V(gravitational potential) against r graph?
Gradient = g
What is the area under the g against r graph?
Area = change in V(gravitational potential)
What is escape velocity?
It is the minimum velocity an object must be given to escape from the large mass when projected vertically from the surface
What is gravitational potential difference?
It is the energy needed to move a unit mass
What are equipotentials?
They are surfaces of constant potentials and no work is done.
There is no lose or gain of energy, therefore, the gravitational potential difference is zero.
What is a satellite?
It is any mass that orbits a larger mass.
What is the relationship between the orbital period and the radius of a circular orbit?
Period squared is proportional to the radius cubed
What is the energy of an orbiting satellite?
The total energy(kinetic and potential) is constant
What is a synchronous orbit?
It is one where the orbital period of the orbitting object is the same as the rotational period of the orbited object.
What are geostationary satellites?
They are a synchronous orbit and always directly above the equator. Their plane of orbit follows the equator.
What are the angular speed and orbital period of a geostationary satellite?
Geostationary satellites have the same angular speed and orbital period as the Earth
What is a geostationary orbit’s orbital radius?
Orbital radius = 42,000km
36,000 above the Earth’s surface
What are geostationary satellites used for?
Sending TV/telephone signals
What are low orbiting satellites?
They are defined as any satellites orbiting between 180-2000km above the surface. Their plane of orbit includes the north and south poles.
What are low orbiting satellites used for?
Communications
Imaging satellites are used for monitoring the weather and spying
