4. Gravitational Fields Flashcards
What is a radial field?
A field in which the field lines are directed towards the centre of mass of an object
What is a uniform field?
A field in which the the gravitational field strength is the same in magnitude and direction throughout the field.
What is gravitational potential?
The work done per unit mass to move a small object from infinity to that point.
What are equipotentials?
Lines of constant gravitational potential.
Define potential gradient
The change of potential per meter at a point in a gravitational field.
What are the assumptions made when using Newton’s law of gravitation between any two point objects?
The gravitational force is
•always an attractive force
•proportional to the mass of each object
•proportional to 1/r^2 where r is their distance apart
Define gravitational field strength
The force per unit mass on a small mass placed in a field
What does each letter mean in the following equation:
F=(Gm1m2)/r^2
F = gravitational force (N)
G = universal constant of gravitation (Nm^2kg^-2)
m1 and m2 = masses of the two objects (kg)
r = the distance between the centre of mass of the two objects (m)
How does the value of g vary with distance from the centre of a spherical planet?
The value of g increases proportionally from the centre of the planet to the surface. The value of g then decreases at a decreasing rate with increased distance from the surface of the planet.
What does the area under a force-distance graph represent?
Work done
This is because work done = force x distance moved
What is a geostationary satellite?
A satellite that stays above the same point on the earths equator. It’s period is exactly 24h and it orbits in the same direction as the earths direction of rotation.
Uses of a geostationary satellite
- communications, including satellite TV’s
- global positioning or GPS
Best for non-interactive systems like TV broadcasts as they are in such high orbit there is a time delay on signals getting there and back, so they wouldn’t be good for things like phone conversations.
What is a geosynchronous orbit?
A satellite with the same orbital period as the earths rotation period.
They appear above the same place on the earth at the same time every day
Uses of satellites in a geosynchronous orbit
- monitoring weather conditions
- communications
- monitoring environmental conditions
They provide continuous monitoring necessary for data analysis
