An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force
Unbalanced forces are not equal and they cause the motion of an object tochange
Reaction force and gravitational force are a balanced pair of forces
Fomula for pressure:
Pressure = force/area
N/m2pascal (Pa)
1N/m2 = 1Pa
common: N/cm2
Larger area - lower pressure (E.g. large tyre - the large area makes the pressure lower, so the vehicle is less likely to sink into the mud)
Smaller area - higher pressure (E.g. sharp knife - the force you put on a knife is more concentrated over a smaller area)
Friction is the force that opposes motion between any surfaces that are in contact
Four types of friction:
static - the friction between two still objects resting on the surface