Module 5.3 - Gravitational Fields ✓ Flashcards
What is a ‘force field’?
A force field is a region where an object will experience a non-contact force
What is the equation for Newton’s law of gravitation?
F = -GMm/r^2
In which way do gravitational field lines point?
In the direction a small test mass would move in the gravitational field
Define gravitational field strength?
Gravitational field strength is the force per unit mass (also called the acceleration due to gravity)
Is gravitational field strength scalar or vector?
Grav field strength is a vector that points towards the centre of the mass you’re looking at (it could be negative if you define the positive direction differently)
Why do those gravity equations have random negatives in them?
r is the distance from the centre of a big mass M, so the positive direction is away from the mass. However attraction is towards the mass so F/g must be -ive
Define gravitational potential
The gravitational potential at a point is the work done moving a unit mass from infinity to that point
What is gravitational potential difference?
Gravitational potential difference is the difference in gravitational potential between two points in a gravitational field
What is the equation for gpe that accounts for changes in g?
change in E = m * (change in Vg)
What is escape velocity?
Escape velocity is the velocity needed by an object to have enough energy to escape a gravitational field
What is the equation for escape velocity?
v = sqrt(2GM/r)
Define a satellite?
A satellite is a small mass which orbits a much larger mass
State kepler’s first law
Each planet moves in an ellipse around the Sun, with the sun at one focus
State kepler’s second law
A line joining the sun to a planet will sweep out equal areas in equal time periods
State kepler’s third law
The period of the orbit and mean distance between the sun and planet are in the relationship:
T^2 <=>< r^3
How are atmospheric thickness and gravity linked?
The more mass a planet has the larger the force further form it’s centre is. This means it can stop more atmospheric particles from escaping into space creating a thicker atmosphere
How do you derive kepler’s third law equation?
The time for one orbit from circular motion is T = 2πr/v
sub in v = sqrt(GM/r) and re-arrange
What is a geostationary satellite?
A geostationary satellite is a satellite that always stays above the same point on the earth’s surface
Where can geostationary satellites orbit?
Geostationary satellites can only orbit along the equator of the Earth (they match the angular speed of the earth to do so)
What is the force distance graph for a point mass in a gravitational field?
F │¦ │ \ │ - - - - - └────── r
