7.2 Gravitational fields Flashcards
What is gravty?
The universal attractive force acting between all matter.
What is the magnitude of gravitational force between two point masses?
(aka Newton’s law of gravity)
What do the letters represent in this equation?
Draw an uniform gravitational field.
Draw a radial gravitational field around a mass.
Define gravitational field strength.
Force per unit mass exerted on a test mass within the field.
What is the magnitude of gravitational field strength in a radial field?
What do the letters represent in this equation?
Define gravitational potential.
The work done per unit mass, moving a test mass from infinity to a specific point.
Why is the gravitational potential always negative?
Gravitational potential is defined as 0 at infinity. Work must be done reach infinity.
Define gravitational potential difference.
The difference in the gravitational potential at two points in a gravitational field.
What is the work done when moving a mass in a gravitational field?
(Moving a mass between two points)
What do the letters represent in this equation?
What is an equipotential surface?
A surface in which every point has the same potential.
Is work done when moving a mass along an equipotential surface?
No.
(Since the potential difference is zero)
Draw an uniform gravitational field with equipotentials.
Draw a radial gravitational field with equipotentials.
What is the equation for gravitational potential in a radial field?
What do the letters represent in this equation?
Define gravitational potential energy.
Component of an object’s energy due to its position in a gravitational field.
What is the gravitational potential energy in an uniform field?
What do the letters represent in this equation?
What is the gravitational potential energy in a radial field.
What do the letters represent in this equation?
Draw the graph of gravitational potential vs distance of a sphere.
What does the gradient of a gravitational potential vs distance graph represent?
Gravitational field strength at a specific point.
Draw the graph of the magnitude of the gravitational field strength vs distance of a sphere.
What does the area of a gravitational field strength vs distance graph represent?
The potential difference between two points
How is orbital period related to orbital radius?
Kepler’s thrid law
What two equations do we equate with each other to start the derivation of Kepler’s third law?
(What force is acting, and what pathis the object taking?)
What do the letters represent in this equation?
During this derivation, what equation do we use to eliminate v?
What do the letters represent in this equation?
What is the total energy of an orbiting satellite?
Total Energy= KE + GPE
What happens to the speed of a satellite when it moves to an orbit closer to the Earth?
As distance decreases, speed increases.
GPE decreases, KE increases
Define escape velocity.
The minimum velocity an object must travel at to escape the gravitational field at the surface of a mass.
How would we find escape velocity?
Consider energy equations
What do the letters represent in this equation?
What is a synchronous orbit?
An orbit where the orbital period is equal to the rotational period of the body being orbited.
(eg 1 day for a synchornous orbit around Earth)
What is a geostationary orbit?
Similar to a synchronous orbit, except the object orbits directly above the same point on the equator.
(Useful for TV phone signals)
What is a low Earth orbit?
Orbital radius between 160km and 2000km
(Useful for monitoring weather, scientific observations)
