| average speed | total distance travelled by an object divided by the total time taken |
| instantaneous speed | the speed of an object measured over a very short period of time |
| displacement | the distance travelled in a particular direction; it is a vector quantity |
| vector quantity | a quantity with both magnitude and direction |
| scalar quantity | a quantity with magnitude only |
| velocity | the rate of change of an object's displacement |
| vector triangle | a triangle drawn to determine the resultant of two vectors |
| resultant vector | the single vector formed by adding together two or more vectors |
| acceleration | the rate of change of velocity of an object; the unit is m/s² |
| constant acceleration | when the change in velocity of an object is the same in the same time period; sometimes called uniform acceleration |
| uniform acceleration | when the change in velocity of an object is the same in the same time period |
| non-uniform acceleration | when the velocity of an object changes by different amounts in the same period of time |
| tangent | a straight like that touches a curve but does not cross it at a point |
| free fall | when an object accelerates due to gravity in the absence of any other forces such as air resistance |
| component | the effect of a vector along a particular direction |
| Newton's second law of motion | resultant force is proportional (or equal) to mass x acceleration/rate of change of momentum |
| weight | the force on an object caused by a gravitational field acting on its mass |
| friction | the name for a resistive force when two surfaces are in contact and tending to slide over one another |
| centre of gravity | the point where the entire weight of an object appears to act |
| uniform motion | the natural state of motion of an object-uniform velocity, constant speed and direction |
| Newton's first law of motion | an object will remain at rest or in uniform motion unless acted on by a resultant force |
| resultant force | the single force that has the same effect as all of the forces acting on an object |
| terminal velocity | the maximum velocity reached by an object falling under gravity or accelerated by a constant force |
| resistive force | a backwards force in the opposite direction to movement caused by friction ot some other viscous force |
| drag | a force that resists the movement of a body through a fluid |
| contact force | the force perpendicular to a surface when two objects are in contact |
| upthrust | the force upwards in a liquid or gas caused by the pressure in the gas or liquid |
| Newton's third law of motion | when two bodies interact, the forces they exert on each other are equal in size and opposite in direction |
| base units | defined units of the SI system from which all other units are derived |
| derived units | units that are combinations of the base units of the SI system |
| newton | one newton is the force that will give 1kg mass an acceleration of 1m/s² in the direction of the force |
| homogenous | equations with the same base units on each side are homogenous |
| mass | the quantity of matter which a body contains |
