Gravitational Fields Flashcards
What does the field line of a gravitational field indicate?
The path which a smaller mass would follow.
What is meant by a radial field?
- where the field lines are directed towards the centre of the mass.
- the force of gravity on a small object near a spherical planet always acts towards the centre of the planet.
What is meant by a uniform field?
- Where the gravitational field strength is the same in magnitude and direction throughout the field.
- The field lines are therefore parallel to one another and equally spaced.
What is the gravitational field strength?
The force per unit mass on a small test mass placed in the field.
What is the gravitational potential energy?
The energy of an object due to its position in a gravitational field.
The position for zero gpe is at infinity.
At the surface, it’s gpe is negative, so it needs to do work to escape from the field completely.
What is the gravitational potential at a point?
The gpe per unit mass of a small test mass.
Equal to the work done per unit mass to move a small object from infinity to a point. (As gpe at infinity is zero)
V = W/m
What are equipotentials?
Surfaces of constant potential.
Therefore no work needs to be done to move along an equipotential surface.
Therefore the gravitational potential energy is constant.
What is the potential gradient?
The change of potential per metre at that point.
The potential gradient = change of V/change of r
NOTE: the gravitational field strength is the negative of the potential gradient.
What is Newton’s law of gravitation?
- The (always) attractive gravitational force is directly proportional to the product of the masses
- inversely proportional to the square of the radial distance between each mass.
What is Kepler’s third law?
When the gravitational force acts as the centripetal force.
T2 proportional to R3
T2 = 4pi^2 x r3 / GM
