2) Gravitational Fields Flashcards
(16 cards)
Explain what is meant by the gravitational potential at a point in a gravitational field.
work done against the field per unit mass when moved from infinity to the point.
State Newton’s law of gravitation.
force of attraction between two point masses is proportional to the product of the masses and inversely proportional to square of distance between them.
Describe and explain what happens to the speed of a satellite when it moves to an orbit that is closer to the Earth.
- speed increases.
- loses potential energy but gains kinetic energy.
State two features of a geo-stationary orbit.
- period is 24 hours.
- equatorial orbit.
State and explain one reason why geo-synchronous satellites would not be suitable for tracking road vehicles.
signal would be too weak at large distance.
State what is meant by the term escape velocity.
-minimum speed given at the earth’s surface that will allow an object to escape the earth’s gravitational field with no further energy input.
State two reasons why rockets launched from the Earth’s surface do not need to achieve escape velocity to reach their orbit.
- energy continually added in flight.
- it is not leaving the gravitational field.
Explain why the values of gravitational potential energy are negative.
- zero potential at infinity.
- energy input needed to move to infinity.
- work done by the field moving object from infinity.
Explain why the values of gravitational potential are negative.
- work done per unit mass in bringing object from infinity to point.
- potential at infinity zero by definition.
- work has been done by the field so potential at all points closer than infinity negative.
Define gravitational field strength and state whether it is a scalar or vector quantity.
- force per unit mass.
- a vector quantity.
Explain why astronauts in an orbiting space vehicle experience the sensation of weightlessness.
- both astronaut and vehicle are travelling at same orbital speed.
- no normal reaction between astronaut and vehicle.
State what is represented by gravitational field lines.
the direction of force on a mass placed in the force field.
What is a force field?
A region in which a body experiences a non-contact force.
Similarity and difference between gravitational and electrostatic forces?
similarity: both have inverse-square laws.
difference: masses always attract, charges may repel.
Formula for gravitational potential energy?
(-)GM/r^2
Formula for gravitational field strength?
Gm/r^2
