4.1 Gravitational field strength

4.2 Gravitational potential

Video - A Level Physics Online - Gravitational Potential

4.3 Newton's Law of gravitation

Video - Isaac Newton's Gravity - part 1 - part 2

Slide show - Newton's law of gravity explained

4.4 Planetary fields

Video - DoodleScience - Gravitational Fields
 
4.5 Satelite motion

Video - Sixty Symbols - Lagrange Points
Podcast - Kepler's Laws of Planetary Motion 
Planetary Motion Simulator
Khan Academy - Astronauts in orbit
Video - Carl Sagan on Keplers Laws

Revision Links - Physics net