Gravitational Fields Flashcards
Define Gravitational Field
A region where an object that has mass, experiences a force
State newton’s law of gravitation and state equation it comes from
Attractive forces between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their seperation
F=GMm/r^2
Define Gravitational Field strength and state the equation it comes from
Force acting on a body per unit mass
G=F/m
Equations for potential energy for uniform and radial field and define potential energy
Uniform, Ep=mgh
Radial = (Gm1m2)/r
Work done in moving object with mass from infinity to that point in the field
Define absolute Gravitational potential energy
Work done per unit mass in moving a body from infinity to that point in Gravitational Field
V=GM/r
Work done = m x V
Derive two equations to show Kepler’s 3rd Law
Derive two equations for equation of orbital velocity
Derive two equations to get equation for escape velocity
Derive two equations for total orbital energy
State times for Low earth orbit (LEO), Medium earth orbit (MEO), High earth orbit (HEO)
LEO : less than 2 hours
MEO : More than 2 hours and less than 24 hours
HEO : greater than 24 hours
Similarity and difference between geostationary and geoschrynous orbits, state advantage of geostationary
Similarity : time period of 24 hours
Differnce : geostationary orbits above same point Earth’s equator
Geoschrynous orbit do not stay above same points of Earth’s surface
Advantage : easier to track
State uses of geostationary orbits
State a little explanation
Monitoring weather : whole earth may be scanned
GPS : several satellites needed to fix position on earth
Communications : limited by intermittent contact
Problem of putting more satellites in orbit
Satellites orbit in closer proximity
Greater risk of collisions
What is meant by satellites in polar orbits
State uses
Satelite passes over north and south poles
Making them ideal for espionage (spying on other countries)
A
Speed = distance / time
Distance = 2.04 x 10^7
Can’t use Kepler’s third law as that gives the orbital of the earth, so your radius would just be equal to radius of earth
D
A
which one has different units to the other 3
a) gravitational potential
b) gravitational field strength
c) force per unit mass
d) gravitational potetnial gradient
State what is meant by terminal velocity
Minimum speed at the Earth’s surface that will allow an object to leave
State two reasons why a rocket does not need the escape velocity to leave the Earth’s surface
- they aren’t given all their Kinetic energy at the Earth’s surface as energy is continually added in the flight
- less energy needed to achieve orbit than to escape from Earth’s gravitational field
Explain why all potential energy values are negative
Zero potential at infinity
Energy input needed to move to infinity
Work done by Field moving object from infinity
Explain how change in potential energy relates to kinetic energy when satellites orbit alters
Loss of gpe is twice gain in kenetic energy
Skip first part calculating force
Explain why astronauts in an orbiting space vehicle experience the sensation of weightlessness
Both astronaut and vehicle are traveling at the same orbital speed
They have the same centripetal acceleration / they are in freefall
No normal reaction between astronaut and vehicle
Explain what is meant by Gravitational potential in at a point in Gravitational Field
Work done against the field per unit mass
When moved from infinity to the point
-63 equals gravitational potential at the surface of the earth
State two features of a geo-sychronous orbit
Period is 24 hours
Remains in fixed position relative to surface of earth
Same angular speed as earth
Equatorial orbit
Signal would be to weak at a large distance
Signal spreads out more further it travels making detection and transmission and less effective
If you have been asked to calculate the gravitational force between two objects and they say calculate the force when the seperation changes, what must you remember to do and not do
D
State what is represented by Gravitational field lines
Direction and magnitude of force on mass placed in the force field
Lines are closer together so field is stronger
Material forming the Earth at K has a higher density than the surrounding material
Only 6.3
Ball will speed up / accelerates when moving towards K because potential at K is lower
In a gravitational field should lines point away or towards object
Towards object, if a ay then it is not a gravitational field
Only 6.6
Should be at right angles and sop and bottom should be symmetrical
The Moonís orbit around the Earth may be assumed to be circular. Explain why no work is done
by the gravitational force that acts on the Moon to keep it in orbit around the Earth.
work = force × distance moved in direction of force
(in circular motion) force is perpendicular to displacement
no movement in direction of force hence no work
Define Gravitational potential difference
The energy needed to move a unit mass between two points in a Gravitational Field
What is an equipotential surface
A surface in which the potential is constant at every point
How are equipotential surfaces found
Through joining points off equal potential together to map out a surface
