1.2 Gravitational Fields and 1.3 Work in a gravitational field

an region in which an object experiences a force (electric = charged object. magnetic = magnetic object)
gravitational field = object with mass experiences a force
all objects with a mass have gravitational field which attracts other objects towards its centre of mass
represented by field lines with arrows that show direction of the force
closeness of lines represents strength
less arrows and larger distance = weaker field = less mass
more arrows and smaller distance = stronger field = more mass
larger force = larger acceleration
arrows closer at the surface than lines further away from the earth = gravitational field is stronger at the surface

in CALCULATIONS - gravitational field strength and gravitational acceleration can be used interchangeably even though they are different conceptually because units workout to be the same

energy transferred to or from an object as a force is applied by another object over displacement
measured in joules (J)
W = Fs
done when F and s are in parallel, or when F has a component parallel to s
a force with a component in direction of object’s movement = positive work
force with component opposite to the direction of object’s movement = negative

as an object falls down, gravitational field it is in does work on it
when object is lifted, work is done on the object is against gravitational field
stronger the field - more work is required

measure of ability to do work
when work is done, energy is transferred from object doing work to object having work done on it
all objects in gravitational field have potential energy based on distance from centre of mass of object producing the field
Ep = mgh
other points of reference (e.g. ground) = zero points - to make calculations easier
energy is a conserved quanity: the total energy (sum of kinetic or potential etc.) does not change