# Engineering Principles V11

Clive W. Humphris

MOTION: Speed, Velocity and Acceleration. If an object moves from one position to another it will have travelled at a certain velocity. This can be calculated by dividing the distance moved by the time taken. The only difference between speed and velocity is the latter defines the direction of movement.

If the object continues to travel at the same speed over twice the distance it is reasonable to expect it to take twice as long. Therefore there is a linear relationship between the variables.

However, if a vehicle travels from one town to another it doesn't always move at the same speed, some of the time it will be stationary or crawling in traffic and so average values must be used. Calculations might not always be at a convenient time or speed. In this case it is the change between two defined conditions that is of interest, i.e. how far did it travel between 2.00pm and 2.45pm clearly the period is 45 minutes. If at the time of measurement the vehicle was already speeding down a motorway then this is taken as an average mph.

Acceleration and deceleration are the rates of increase and decrease in velocity over time (unit of measurement is m/s²). 