Chapter 4 - Gravitational Fields Flashcards
Give one property that is always true for a gravitational field
It is attractive
What is gravitational field strength?
The force on a unit mass when it is put in a gravitational field- (g=F/m)
What is a gravitational field?
A force field around a mass
Two bodies near each other will do what?
Exert equal and opposite forces on each other
What is the weight of an object?
The force of gravity acting on the object giving it it’s mass
What is a radial field?
A field in which the field limes are straight and converge towards a central point (the centre of a circle)
What is a uniform field?
A region where the field strength is the same magnitude at every point in the field
Describe the field lines in a uniform field
Parallel and equally spaced
Describe how the magnitude of ‘g’ changes in a radial field
‘g’ decreases when the distance from the massive body increases
What is the unit of gravitational field strength?
Nkg^-1
What is gravitational potential?
The work done per unit mass to move a small mass from infinity to a point
(V=W/m)
What happens to your gravitational potential as you move away from the Earth?
Your gravitational potential energy (GPE) increases
What is your gravitational potential when you are in deep space?
Zero - provided that there a no large masses nearby
What is the unit of gravitational potential?
Jkg^-1
What are equipotentials?
Lines of constant potential around a point mass
What happens to the gravitational field of the Earth as you move away from it?
The gravitational field becomes weaker
What happens to the spacing between the equipotential lines as you move away from the Earth?
They become more spaced out
What does it mean if field lines are concentrated in a small area?
It means that the field strength is strong - field strength is strongest when field lines are closest
What is the potential gradient of a gravitational field?
Change in potential per unit distance
Potential Gradient= change in V/change in r
How are gravitational field strength and the potential gradient linked?
‘g’ is the negative of the potential gradient
g=-V/r
State Newton’s law of gravitation
The gravitational force between two point objects is proportional to the product of the two masses and inversely proportional to the square of the distance between them
Which direction do the field lines around a spherical mass act?
Towards the centre of the sphere
Why is the gravitational field strength zero at the centre of a spherical mass?
Inside the sphere, as r becomes smaller, less mass contributes. Only the mass within the radius will contribute to the field strength. At the centre, the mass which contributes to g is zero. As g=GM/r^2, if M=0 then g=0.
Inside the sphere, as r becomes smaller, less mass contributes . Only the mass within the radius will contribute to the field strength. At the centre, the mass which contributes to ‘g’ is zero
As ‘g’=GM/r^2 If M=0 then g=0
What is the formula for gravitational potential around a spherical mass?
V=-GM/r
Where does a geostationary satellite orbit, in respect to the Earth?
It orbits directly above the equator
What is the time period of a geostationary satellite?
24 hrs
What is a satellite?
A small mass which orbits a larger mass
What provides the centripetal force for an orbiting satellite?
Gravitational Attraction (Gravitational Force)
What are geostationary satellites used for?
Communications
What is polar orbit?
Low Earth orbit around the poles of the Earth
Why are weather satellites situated in polar orbits?
Polar orbits are closer to the Earth so the satellite will have a shorter time period than the Earth. As it orbits the Earth several times in one day, it can track weather patterns over a wide area.
Why are geostationary satellites not suited for tracking weather conditions?
They are too far away from the Earth. As they have the same time period as the Earth, they are continually above the same point of the Earth - this means they can only track a limited area, not a broad area.
What is the time period of a polar orbit?
Between 1.5-3 hrs
