1. Gravitational fields
1.1. acts on masses
1.1.1. always attractive
1.2. Newtons law of gravitation
1.2.1. The force of attraction between two point masses is proportional to the product of the masses and inversely proportional to the square of their separation
1.2.2. The force between two spherical masses whose separation is large compared to their radii is the same as if the two spheres were point masses with their masses concentrated at the centres of the spheres
1.3. gravitational field strength
1.3.1. force per unit mass on a point mass at that location in the field
1.3.2. vector quantity
1.3.3. unit newtons per kilogram
1.3.4. g=F/m
1.3.5. the expression for gravitational field strength at the surface of a planet is derived by equating F= gm and newtons law of gravitation
2. Electric fields
2.1. acts on charges
2.1.1. attractive and repulsive
2.1.2. two types of charge, positive and negative
2.1.2.1. in an isolated system the quantity of charge is always conserved
2.1.2.2. conductors have lots of free (very loosley bound to atoms) electrons which will move when an electric field is applied
2.1.2.3. insulators don't have lots of free electrons. The electrons can sometimes be removed by friction
2.2. coulombs law
2.2.1. the force between two point charges is proportional to the product of their charge and inversely proportional to the square of their separation
2.3. electric field strength
2.3.1. the force per unit charge that a positive point test charge would experience at that point in the electric field
2.3.2. vector quantity
2.3.3. Unit - Newtons per Coulomb
2.3.4. E = F/q
2.4. electric field patterns for different charge configurations
2.4.1. unequal charges
2.4.2. equal charges
2.4.3. arrow shows the direction of force that a positive test charge would experience in the field
3. magnetic fields
3.1. acts on magnetic materials
3.1.1. attractive and repulsive
3.2. moving charges produce magnetic field
3.2.1. field around a current carrying wire
3.2.2. field around a solenoid
3.2.3. the force on a current carrying conductor in a magnetic field