### Scalars and Vectors

Any object that is acted upon by an external force will respond to that force by moving in the line of the force. However, if two or more forces act simultaneously, the result is more difficult to predict; the ability to add two or more vectors then becomes important.

The time taken to fill a water tank may be measured as, say, 50s. Similarly, the temperature in a room may be measured as, say, 16oC, or the mass of a bearing may be measured as, say, 3 kg.

Quantities such as time, temperature and mass are entirely defined by a numerical value and are called scalars or scalar quantities.

Not all quantities are like this. Some are defined by more than just size; some also have direction. For example, the velocity of a car is 90 km/h due west, or a force of 20N acts vertically downwards, or an acceleration of 10m/s2 acts at 50o to the horizontal.

Quantities such as velocity, force and acceleration, which have both a magnitude and a direction, are called vectors.

Scalar Quantities Vector Quantities
Length, Area, Volume Displacement, direction
Speed Velocity
Mass, Density Acceleration
pressure Momentrum
Temperature Force
Energy Lift, Drag
Entropy Thrust
Work, Power Weight