Grav Fields P2 Flashcards
What is the magnitude of the gravitational force of two objects proportional to?
The mass of both objects
What is the magnitude of the gravitational force of two objects inversely proportional to?
The distance from the centre of both objects squared (Inverse square law)
What is a point mass?
Where the mass is concentrated at a single point
What is gravitational field strength?
The gravitational force per unit mass of a test mass
What is a test mass?
A particle with a very small mass used to test a gravitiational field without affecting it
What is gravitational potential energy?
The amount of energy/work done required to move a mass from infinity to a given point in a gravitational field
What is gravitational potential energy at infinity?
Zero
What happens to the GPE as it gets closer to the source mass?
The more negative the GPE becomes
What is escape velocity?
The minimum velocity required for an object to move from a point in a planet’s gravitational field to a point where the gravitational field is negligible.
What is gravitational potential?
The work done to move a 1kg mass from infinity to a point in the field
What are equipotentials?
A set of points which have the same gravitational potential
What is potential gradient?
The change in potential per unit distance at that point.
What does the area between two points below a gravitational field strength graph tell us?
The gravitational potential difference
At what seperations are equipotentials when the gravitational field strength is high?
Large seperations
What do satellites do in low Earth orbits?
They move over lots of different points on the surface and orbit relatively close to the surface
What do satellites do in geostationary orbits?
They appear to stay still in the sky over a single point on the surface and orbit at distances relatively far from the surface
How do you derive the escape velocity?
Set the equations of kinetic energy and gravitational force equal to each other
What is the formula for the total energy of a satellite?
-GMm/2r
Why is gravitational potential difference a negative value?
Because work needs to be done to move an object from the inside of the field to the outside. Since infinity is zero, below infinity must be negative
How is the orbital period realted to the radius of a circular orbit?
T^2 = k x r^3
How could you find the speed of an orbiting satellite?
Set the centripetal force to the gravitational force and sub in v=2πr/T
