Question

Why is speed considered to be an incomplete quantity to describe motion? Name a quantity that describes motion completely.

Answer 1

1. When a body is travelling, we can identify the position of the body with respect to the time taken to travel by measuring its distance travelled, speed, velocity etc.
2. Speed is a scalar quantity which tells us how fast or slow an object is moving.
3. As speed does not talk about the direction in which we are travelling.
4. Hence it is an incomplete quantity to describe motion.
5. It is defined as the ratio of distance travelled by the time taken.
6. $speed=\frac{dis\tan ce}{time}$
7. So, the correct quantity which describes the motion is velocity which is defined as Speed with direction.
8. Velocity tells us how fast or slow an object is travelling in a particular direction.

Hence, the correct quantity which describes the motion is velocity which is defined as Speed with direction.