A physical quantity is one that can be measured, or calculated, and expressed in numbers.
Physics is about laws, measurements and calculations. In order to describe any observa- tions we must describe what physical quantities are being measured. All quantities have magnitude (size); some also have direction.
Scalar Quantities SCALAR QUANTITIES A scalar quantity is one with magnitude only. It has no directional component.
SCIENCE,TECHNOLOGY & SOCIETY Examples of scalar quantities Table 2.1: Examples of scalar quantities
length area
volume speed
Distance DISTANCE
The distance (s) between two points is a measure of how far one point is from the other.
b s a Fig 2.1: Straight line distance between two points 12 INVESTIGATING PHYSICS
Distance is often referred to as length (l) as the two terms have more or less the same meaning.
They are both scalar quantities with an SI unit of metre (m).
For many of the experiments we come across in Leaving Cert. Physics, length is measured using a metre stick. When dealing with small distances, other instruments such as a Vernier callipers or a micrometer can be used.
