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Module 5 - Chapter 18 - Gravitation fields II - Coggle Diagram
Module 5 - Chapter 18 - Gravitation fields II
Satellites
Putting into orbit
For any satellite in orbit, the gravitational force is
Satellite is always falling towards earth, but it travels such a great distance that as it falls, the earth curve away betwen it, so it stays at the same heigh
For any satellite, the correct speed for a stable orbit at distance r is
mass of satellite isn't a factor, all satellites place at a given hight travel at the same speed as there is no air resistane so speed remainst constant
Uses
Communications - satellite phones, TV
military - reconnaissance
research - down on earth and universe
weather and climate - monitoring weather
Orbit types
Polar orbit
circles the poles
complete view of earth over a given period period as earth rotates beneath satellite
Satellite covers all parts of the globe eventually
low earth orbit
Satellites in orbit close to earth
Orbits can take less than 2 hours (kepler's 3rd law)
Geostaionary
As height increases, so does its period
Remains over the same point of the earth whilst it rotates
Satellite must be above the eqation, rotate in the same direction as earth and have an orbital period of 24 hours
Gravitational potential
Work done per unit mass to move an object to that point from infinity, units of Jkg^-1
Infinity is a distanc so far from the field producing object that the field strength is 0
All mass attracts eachother, it takes energy to move objects apart. Gravtational potention is max at infinity, where its value if 0
All values are negative
If the gravitational potential is -20MJKg^-1, it required 20,000,000 J to move a unit mass from that point to infinity
radial field
Gravitational potential at any point in a radial field aorund a point mass depend son the distance from the point mass and the mass of it
Graph of Vg against r
Potential tends to 0 as r approaches infinity
Smallest value of r equals the radius of earth
Vg against 1/r
Straight line through the origin
Gradient equal to -GM
Changes in gravitational potential
Moving towards a point mass results in a decrease in gravitational potential (more negative)
Moving away (to infinity) results in an increase in gravitational potential (less negative )
Since gravitational potential is scalar, total gravitational potential at any point equals the algebraic sum of the gravitational potentiel from each mass at that point
Gravitational potential energy
Work done to move the mass from infnity to a point in a gravitational field
Uniform field
To change the gravitational potential energy of an object, its height above the surface must be changes, this causes a change in gravitational potential, and gpe
A to B increases gravitational potential energy, object gains gravitational potential energy
A to C - no change
B to A - decreases in gravitational potential energy energy
Radial field
A to B - gravitational potentiel decreases, so does the gravitational potentiel energy - transferred into kinetic
Force against distance graph
Area under a force distance grpah equals the work done on the object
Work done to move a mass from A to B is the shaded part
Work done can be negative if object falls
Escape velocity
Object must be supplied with enough energy equal to the gain in potential energy needed to lift it out of the g field
If we ignore air resistance, the kinetic energy of the projectile is transferred into gravitational potential energy as it rises
loss of kinetic must equal the gain in gpe
Minimum velocity to do this is escape velocity
Same for all objects on a given planet regardless of mass
