Scalar Quantities.

A scalar quantity has magnitude (size) only and no direction. Examples include distance, speed, mass, time, volume, density, energy and temperature.Scalars are added using ordinary arithmetic. A mass of 2 kg added to a mass of 3 kg always gives 5 kg, whichever way the masses are arranged.Many scalar quantities come in pairs with a vector. Distance is a scalar, but displacement, which is distance in a particular direction, is a vector. Speed is a scalar, but velocity is a vector.Quantities such as mass, distance and speed cannot be negative. When a scalar has a sign, such as a temperature in °C or a charge, the sign is part of its value, not a direction.To decide whether a quantity is a scalar, ask whether it makes sense to give it a direction. It makes sense to say a force acts to the left, but not that a mass or a time does.