3.7.2 - Gravitational Fields Flashcards
What is gravity?
Universal attractive force between all matter.
What are gravitational fields?
A region of space which any mass will experience a force of attraction.
What is the gravitational field strength?
The force per unit mass on a small test mass placed in the field.
What indicates the strength of a field?
The separation of the field lines.
What does the law of gravitation show about the relationship between field strength and radius?
F is proportional to 1/r^2
What is gravitational field strength, g, measured in?
Nkg^-1
What is gravitational potential?
The GPE that a unit mass at that point would have.
When does gravitational potential = 0?
At infinity.
When is gravitational potential negative?
On the surface of the mass. It increases with distance from the mass.
What is gravitational potential, V, measured in?
Jkg^-1
Under what graph is V?
A g r graph.
What does Ep =
-GMm / r
What does Ek =
GMm / 2r
What does total energy =
-GMm / 2r
What are equipotentials?
Lines which connect points of the same gravitational potential.
How does work done change as you go across an equipotential?
It doesn’t - no work is done.
What is a potential gradient?
The change in potential in a gravitational field per metre (V/r)
What force keeps satellites in orbit?
Centripetal force.
What is the relationship between the radius of a orbit and the time period?
T squared is proportional to r cubed.
In an elliptical orbit what happens to the speed as the radius decreases?
The speed increases as does the KE. The GPE decreases.
What remains constant in orbits?
The total energy (GPE + KE)
What is the escape velocity?
The minimum velocity required for an object to escape from the planet when fired vertically from the surface.
What does escape velocity =
root (2GM/r)
What is a synchronous orbit?
When an orbiting object has an orbital period equal to the rotational period of the object it is orbiting.
What is an example of geostationary satellite an example of?
Synchronous orbit as they are always in the same place above earth.
Where are geostationary satellites positioned?
Above the equator.
What are geostationary satellites used for and why?
Used for sending TV and telephone signals as the satellite is stationary relative to earth’s position, so you don’t have to alter the angle of your receiver to keep up with the position of the satellite.
What are low orbiting satellites used for any why?
Used for communication as they are cheaper to launch and require less powerful transmitters as they are closer,. Also used for mapping, monitoring and the weather.
Why are low orbiting satellites used for mapping?
As they are positioned in the plane of the north and south poles and because they rotate at a different angular speed to the earth, the satellite doesn’t stay over the same part of the earth and so the whole surface can be scanned.
