Describe the characteristics of a scalar quantity.

A scalar quantity is characterised by having only magnitude and no direction.

In physics, quantities are often classified into two categories: scalar and vector. Scalar quantities are those that are fully described by a magnitude alone. The magnitude of a scalar quantity is a numerical value with an appropriate unit. They are not concerned with direction, unlike vector quantities. Scalar quantities are often used in physics to describe things like temperature, time, mass, energy, and speed.

For instance, if we say a car is moving at 60 km/h, we are describing its speed, a scalar quantity. We are not concerned with the direction the car is moving in. Similarly, if we say an object has a mass of 10 kg, we are describing a scalar quantity. The mass of an object doesn't depend on which way it's oriented or where it's located.

Scalar quantities can be added, subtracted, multiplied, and divided in the usual way we perform arithmetic operations. For example, if you travel 5 km to the north and then 3 km to the south, your total displacement is a vector quantity of 2 km to the north. However, your total distance travelled, a scalar quantity, is 8 km.

In addition, scalar quantities can have either positive or negative values. For example, an increase in temperature can be represented by a positive change, while a decrease in temperature can be represented by a negative change.

In summary, scalar quantities are an essential part of physics, providing a simple and straightforward way to quantify the properties of objects and phenomena. They are characterised by having only magnitude, without any associated direction.