Gravitational fields Flashcards
what is a force field
an area that experiences a non-contact force
what is a gravitational field
an area where an object with mass experiences an attractive force
what are field lines
Represent a field visually, they tell you the direction of the force acting at that point in the field. dense lines indicate a stronger field.
what is a radial field
it means all the lines meet at the centre of mass, implying the field is weaker the further way from the centre. earth has a radial gravitational field.
what is a uniform field
where all the field line are parallel, implying field strength is constant. this is considered to be the case at an objects surface
how is field strength and distance to the centre related
its an inverse square law
what is newtons law of gravity
allows you to calculate force in a gravitational field.
-its proportional to the product of the masses
-its inversely proportional to the square of the distance
-its always attractive
what is gravitational field strength
the force on an object per unit mass
how does gravitational field strength relate to distance graphically
1/x^2
from 9.81 on the graph
doesnt reach 0
what is gravitational potential
the energy required (work done) to move a 1kg mass from infinity to a point in the field
what are equipotential lines
when putting values of V on a map they look like contour lines, which are at right angles to the gravitational field lines
why is gravitational potential negative
because at infinity, GPE=0 and g=0. so as you fall further from infinity you gain g, and therefore GPE. so moving toward it means you have negative GPE as its a vector.
what does gravitational potential against distance look line on a graph
-1/x
starts at -62.5
doesn’t reach 0
what does the gradient mean on a gravitational potential against distance graph.
gravity
a tangent will need to be drawn
what is gravitational potential difference
if you want to move an object close of further from earth then you need to move between equipotential lines
earth=62.5MJ ISS=60.6MJ diff= 1.9MJ
for every 1kg you want to move it will take 1.9MJ
why does a satellite do no work
it moves along an equipotential line, so the gravitational potential different is 0
what is the equation for gravitational potential energy
Ep=-GMm/r
how to do you calculate gravitational difference from a field strength against distance graph
area underneath it
what is a low earth orbit
between 200-2000km
around 2 hour time period
used for weather satellites
can be at an angle to the equator.
what is a geostationary orbit
at 35000km
exactly 24 hour time period, will remain at the same point above earth
in line with the equator
used for communication
what are polar orbits
when an orbit is at 90 degrees to the equator.
every time it fishies an orbit it will be over a new part of earth making it idea, for scanning it.
however you need a lot of satellite dishes with moveable heads to track it.
what is a synchronous orbit
when the orbiting object has the same period equal to the body its orbiting
what is a geosynchronous orbit
an orbit with the same time period as earth (24 hours)
why is orbital speed different for different objects
a closer satellite to an object must go faster due to a much stronger gravitational force. so it will need a much higher horizontal velocity
