## Overview This topic examines the similarities and differences between electrostatic and gravitational fields. The ideas of potential and potential energy in fields of force are introduced. ## Mathematical Skills There are a number of opportunities for the development of mathematical skills in this unit. These include recognising and making use of appropriate units in calculations; recognising and using expressions in decimal and standard form; using calculators to find and use power, exponential and logarithmic functions; using calculators to handle sin x, cos x, tan x when x is expressed in degrees or radians; making order of magnitude calculations; changing the subject of an equation; translating information between graphical, numerical and algebraic forms; drawing and using the slope of a tangent to a curve as a measure of rate of change; interpreting logarithmic plots; using Pythagoras’ theorem, and the angle sum of a triangle; using sin, cos and tan in physical problems, using small angle approximations including sin   , tan   , cos 1   for small θ where appropriate. ## How Science Works There are opportunities within this topic for learners to analyse and interpret data to provide evidence, recognise correlations and causal relationships. Learners can be given the opportunity to use theories and models to predict the motion of satellites and planets. Applications and uses such as geostationary satellites can be studied and their benefits and risk evaluated as well as the ethical issues involved in their use. ### Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the features of electric and gravitational fields as specified in the table on page 30 (b) the idea that the gravitational field outside spherical bodies such as the Earth is essentially the same as if the whole mass were concentrated at the centre (c) field lines (or lines of force) giving the direction of the field at a point, thus, for a positive point charge, the field lines are radially outward (d) equipotential surfaces joining points of equal potential and are therefore spherical for a point charge (e) how to calculate the net potential and resultant field strength for a number of point charges or point masses (f) the equation ΔUP = mgΔh for distances over which the variation of g is negligible ![[Electric vs static fields.png]]