Question

In physics, quantities are classified as either scalars or vectors. What property or properties completely describe a scalar quantity?

Hint:

Ask whether it makes sense to assign a direction to the quantity. If not, only its size or magnitude is needed to describe it.

Answer 1

Step 1: Physical quantities are grouped into scalars and vectors based on whether direction matters for them or not.

Step 2: A scalar quantity is one that is completely specified by giving only its magnitude, that is, a number together with an appropriate unit. It has no direction associated with it at all.

Step 3: For example, if we say the mass of an object is 5 kilogram, the temperature of a room is 30 degree Celsius, or the speed of a car is 60 kilometre per hour, each of these statements fully describes the quantity. There is no need, and no meaning, in asking which direction the mass or the temperature points in.

Step 4: Other common examples of scalar quantities include time, distance, energy, work, power, density, and electric charge. All of these are added, subtracted, multiplied, and compared using ordinary arithmetic, since they carry only a size, not a direction.

So a scalar quantity is completely described by its magnitude alone.