SQA National 5 Physics

## Two kinds of quantity A **scalar** quantity has a size (magnitude) only. A **vector** quantity has a size and a direction. Saying that a runner has travelled 400 m tells you how far, and saying she has moved 400 m due north tells you where she has ended up relative to where she started. The first is a scalar statement and the second a vector one. | Scalar | Vector | |---|---| | distance | displacement | | speed | velocity | | mass | force | | time | acceleration | | energy | | Distance is the total length of the path taken. **Displacement** is the straight-line distance from the start to the finish, in a stated direction. A lap of a 400 m track gives a distance of 400 m but a displacement of zero, because the runner finishes where she began. Speed is how fast something is moving along its path, whereas **velocity** is speed in a stated direction, so a car going round a roundabout at a steady 10 m/s has a constant speed and a changing velocity. Direction is given as a compass point, as a bearing (an angle clockwise from north, written with three figures such as 053), or as an angle to a stated line. A vector pointing one way is given a positive sign and one pointing the opposite way a negative sign when the motion is in a straight line. ## Adding vectors: the resultant The **resultant** of two or more vectors is the single vector that has the same effect as all of them together. Vectors are added tip to tail. ### In one dimension When the vectors point along the same…