Year 2- Gravitational Fields Flashcards
what do all objects with a mass exert
a gravitational force on each other
what is the gravitational force a mass experiences near the surface of a planet or moon
weight
what is the equation for weight
W = mg
what is the gravitational force proportional to when 2 masses are involved
directly proportional to the product of the 2 masses, and inversely proportional to the distance between the two centres squared
how can we assume an object can act like a point mass
if it is spherical and has uniform density
define point mass
the object acts like all the mass is concentrated in the centre
when dealing with masses in a gravitational field, what is assumed
all the masses are point masses
what are all masses surrounded by
a gravitational field
where will all masses feel a force
in the gravitational field
what is gravitational field strength
the gravitational force per unit mass a mass will experience in a field
what is the source of a gravitational field called
a source mass
how can we test the field due to a source mass
using a test mass
what is a test mass
a small enough mass that won’t effect the field
is gravitational field strength vector or scalar
vector, with the direction towards the source mass
define gravitational field strength in terms of the equation
gravitational field strength is directly proportional to the mass of the source mass, and indirectly proportional to the distance between the centre of the test mass and source mass squared
how can the gravitational field strength be represented
-with vectors pointing in the direction of the field, with different lengths of the vectors representing different field strengths
-with field lines pointing in the direction of the field, and the distance between the field lines representing different field strengths
what is the shape of field lines around a spherical mass
radial
what does a radial field represent in terms of gravitational field strength
it decreases as you get further from the centre point mass
how can we represent the gravitational field close to the surface and what does it mean
as a uniform field, therefore g is a constant
how do you differentiate between what equation to use for the force
w=mg for when the mass is close to a planet
f=gmm/r^2 for when the distance is a lot greater (where g would not be a contstant)
how can you find the point between two masses where their each individual fields cancel out
take g=0
how can you find the direction/ force of a point in 2 gravitational fields
find the resultant force vector
what does the graph of g against r look for a point mass
a decreasing curve
what does the graph of g against r look for a planet
a positive linear line up to the surface of the planet, that rapidly changes to a decreasing curve
when a mass is in a uniform gravitational field, how can you calculate the change in potential energy
GPE=mgh
what is the gravitational potential energy closer than infinity in a radial field
less than 0
define gravitational potential energy
the work done to move a test mass from infinity to a given point in the field
when is Ep=GMm/R used and when is Ep=mgh used
Ep=GMm/R is used to find absolute values in a radial field
Ep=mgh is used to calculate changes in a uniform field
what is the total potential energies of a test mass in 2 gravitational fields
the sum of the gravitational potential energies due to the individual gravitational fields, it is never 0
what is the work done to move a test mass from one point to another
the change in gravitational potential energy between the two points
is the work done positive or negative when a test mass is moved away from the source mass
positive
what is the gravitational field for an object to escape the field into deep space
0/ negligible
how much kinetic energy does an object need to escape the field
an amount equal to the magnitude of the gravitational potential energy
what equation can be used to solve for the escape velocity
o.5mv^2=GMm/R
what is escape velocity
velocity an object needs to escape a gravitational field
