Section 7.1 Gravitational Fields Flashcards
What is a test mass?
A mass that has a negligible affect on the field
Define gravitational field strength
The force per unit mass
Show how acceleration is equal to the gravitation field strength when a mass is in free fall
a = F/m
a = gm/m
a = g
What is the unit of g?
N/kg
What does gravity affect?
Masses
What is a field line?
The path that a mass would take when placed in a gravitational field
What is a uniform field?
A field where the field strength is constant
What is a radial field?
Field strength is proportional to 1/r²
What is gravitational potential energy?
The work done moving a mass from infinity to a distance r away from the centre of the field
Why is gravitational potential energy negative?
because the potential energy at infinity is 0
What is gravitational potential?
The work done moving a mass from infinity to a distance r away from the centre of the field
What is an equipotential?
A surface of constant potential
True or false equipotentials are at right angles to field lines?
True
What is the eqaution for force in a radial field?
F = -G.M.m/r²
What is the equation for gravitational field strength in a radial field?
g = -G.M/r²
What is the equation for work done in a radial field?
W= -G.M.m/r
What is the formula for gravitational potential?
V = -G.m/r
What is the relationship between Force and work done?
Work done is the area under a force vs r graph
What is the relationship between gravitational field strength and gravitational potential?
Potential is the area under a field strength vs r graph
What is Keplers 3rd law?
- T² α r³
- square of the orbital period is directly proportional to the cube of the radius
What is the formula for orbital velocity?
v= √G.M/r
How is formula for orbital velocity derrived?
By equating force in radial field to centripetal force
What is the formula that shows the formula for keplers 3rd law
T² =(4π/G.M).r³
What is newtons law of gravitation?
- Gravity acts on any objects which have mass and is always attractive.
- force between two masses is directly proportional to the product of the masses
- inversely proportional to the square of the distance between them
- Modelled on point masses
How is the formula for keplers 3rd law derived?
Equating force ina radial field and centripetal force
What is the eqaution for escape velocity?
v = √ 2GM/r
What is escape velocity?
the minimum velocity it must travel at, in order to escape the gravitational field at the surface of a mass
How is the formula for escape velocity derrived?
Equating work done formula in a radial field and kinetic energy
What is the total energy of a satelite?
Total energy of a satellite = kinetic energy + potential energy
What is the formula for total energy of a satelite?
E = -GMm/2r
What is a synchronous orbit?
the orbital period of the satellite is equal to the rotational
period of the object that it is orbiting,
What is geostationary satellite?
they always stay above the same point on the Earth
features of a geostationary satelelite?
Orbital period matches Earth’s rotational period exactly
Satellite maintains same position relative to Earth
Only one particular orbit radius is possible
Travels west to east above Equator (in same direction as Earth’s
rotation)
Orbit height is greater than polar orbit satellite
Speed is less than that of polar orbiting satellite
Scans a restricted (and fixed) area of the Earth’s surface only
Applications: telecommunications generally, cable and satellite
TV, radio, digital information, etc.
Satellite is in continuous contact with transmitting/receiving aerial
Aerial can be in a fixed position
