1. 1.2.7-9 gRavitational fields and newton

2. 1.2.7 Newton’s Law of Gravitation - 2
Objectives
Select and apply the equation for gravitational field strength.
Explain the nature of the gravitational field strength close to the Earth’s surface.

3. g = GM/r2 An object in free fall in this case weight =mg
Gravitational attraction
F = GMm/r2
Therefore mg = GMm/r2
And so
g = GM/r2
Therefore the gravitational field strength decreases with distance from a planet and depends on the Mass of the planet

4. Falling objects near the Earth

5. Weightless or not?

6. This person cannot be weightless!
Why not? Because gravity is pulling them to the centre of the Earth.
If you said no it may be because you know you could feel the wind on you in this situation!?

7. Training to deal with weightlessness – where??
On a converted Boeing 747 diving straight down at about 125 plus miles per hour so you are falling down to Earth at the same speed as the plane.
This means you can effectively move around as though you were weightless in space but without the hassle or cost!

8. Still not weightless! Gravity is still pulling you in to the Earth BUT you are trying to fall off the edge of the world but Gravity keeps on pulling you back in!
We feel weightless because our body is used to supporting itself using our muscles.
If we no longer need to do this, as in free fall or that moment on a roller coaster, then we will experience a moment of “weightlessness”.
This could not actually be the case on the shuttle or it would fly off into space rather than going in a circle!!

9. 1.2.8 Planetary orbits

12. 1.2.9 Satellites Objectives
Define geostationary orbit of a satellite and state uses of such satellites
Calculate the radius of a geostationary orbit

13. Geostationary satellites
Must be over the equator and remain over the same point on the surface
Have an orbit centred on the Earth’s centre
Be travelling West to East (same way the Earth spins)
Have a period of 24hours
Using Kepler’s third law you can prove there is only one altitude where this can occur of approximately 36,000km.
The general use of these is Telecomms but they are expensive due to the energy needed to get them to that location.
Drawbacks are that the power is spread over a large area and therefore huge amounts of power transmitted. However it does mean a large area of land can be covered by one satellite transmisson!

14. Geosynchronos satellites
May only be 500km above the surface
Have to be tracked as they move relative to the Earth
Are less expensive to put in orbit
Can provide greater detail of the surface
Higher energy levels can be received on the Earth
Used for weather, spying, mapping and GPS