Gravitational fields Flashcards
Everything you need to know to get A* in OCR Physics A Level, closely following the specification and the textbook
What is a gravitational field?
A field created around any object with mass, extending all the way to infinity
How do gravitational fields come about?
Any object with mass created a gravitational field around it
How are masses of spherical objects in a gravitational field modelled?
The mass is modelled as a point mass at its centre
In what direction do gravitational field lines act?
Towards the centre of the mass
What is the equation for gravitational field strength?
g = F/m
What is Newton’s Law of gravitation?
F = -GMm/r^2
What is the equation for the gravitational field strength of a point mass?
g = -GM/r^2
Define a uniform gravitational field
A gravitational field in which the field lines are parallel and equidistant, and the value of g remains constant
What is Kepler’s first law?
The orbit of a planet is an ellipse with the Sun at one of the two foci
What is Kepler’s second law?
A line segment joining a planet and the Sun sweep s out equal areas during equal intervals of time
What is Kepler’s third law?
The square of the orbital period T of a planet is directly proportional toe the cube of its average distance from the Sun
What is the centripetal force?
The net force on a body in orbit, which acts perpendicular to the direction of the velocity, towards the centre of the circle of orbit
What is the centripetal force provided by?
It is provided by the gravitational force between the body in orbit and the Sun (star)
Where do Kepler’s Laws apply?
Everywhere, they are not limited to our solar system
What are the two types of artificial satellites?
geostationary and polar
What are the conditions for a satellite to be in a geostationary orbit?
Satellite must be in orbit above the Earth’s equator, must rotate in the same direction as the Earth’s rotation, and must have an orbital period of 24 hrs
What are some uses of geostationary satellites?
Communications, Research, Weather and Climate.
What is the gravitational potential?
The work done in bringing a unit mass from infinity to a specific point
What is the gravitational potential at 0?
infinity
What happens to the gravitational potential when moving away from the point mass?
Results in an increase in the gravitational potential
What is the escape velocity?
The minimum velocity at which an object has just enough energy to leave a specified gravitational field
What is the equation for the escape velocity?
v = sqrt(2GM/r)
Define the gravitational field strength
The force per unit mass at a point in a gravitational field
