gravitational fields Flashcards
what is gravity?
a force that acts between any 2 masses
does the gravitational force attract or repel
attract
when does the gravitational force increase
increases nearer the 2 bodies or when the bodies have large mass
what happens to gravitational field as you move away from the object
strength of field reduces
what direction does gravitational force act towards
always downward towards centre
what is newtons law of gravitation
- force is directly proportional to the product of the masses
- force is inversely proportional to the square of the separation between 2 masses
what does closer Field lines mean?
closer the field lines are together the denser the gravitational field
what is escape velocity
escape velocity refers to the minimum velocity an object must reach to break free from the gravitational attraction of a massive body, such as a planet or a star
if KE = PE
no friction resistance
= escape from earths gravitational pull
how is a satellite put into orbit
by accelerating it to a sufficiently high tangential speed
what happens if satellites speed is too high?
it will escape
what happens if satellites speed is too low?
it will return to earth
what is Keplers 3rd law
the square of the orbital period of a planet is directly proportional to the cube of the seperation distance.
what is a geostationary satellite
the satellite appears to remain stationary relative to a fixed point on the Earth’s surface, and it orbits the planet above the equator in the same direction as the Earth’s rotation.
what are the two types of fields
radial field and uniform field
what is gravitational field strength
attractive gravitational force that a unit mass would experience at a given point in the field
GFS equation for uniform field
g = F/M
GFS equation for radial field
g = GM/r^2
what is gravitational potential
amount of work done in moving a unit mass from infinity to a given point in a gravitational field
what is gravitational potential at infinity
zero
what is the work done for gravitational potential
work is done to move an object closer to the field and so gravitational potential is always a negative value
what are equipotentials
planes containing points with equal gravitational potential. this means that the amount of work done when an object is moved around these planes is zero
what is a synchronous orbit
have a time period of one day and so return to the same place In the sky each day
what is a low orbit?
orbit at heights of between 160km and 2000 km
what is a geostationary orbit
have a time period of one day and stay over the same point on the earths surface,
must be directly placed above the equator and travel in same direction as earths rotation
what is an equipotential surface?
a surface in which every point on the surface has the same potential
why is the gravitational potential a negative value?
work needs to be done to move an object from the inside of the field to the outside
since outside the field’s potential is defined as 0 then the potential inside the field must be negative
compare the PE and KE of a lower orbit to a higher one
lower orbit (smaller mass) has potential energy and more kinetic energy than a higher orbit (bigger r)
