Speed is just how fast something is moving. But what does it mean when we ask how fast something is moving? It means how much distance that object is covering in some time.
Speed can also be defined as the rate at which the distance is covered compared to the time passed. Rate is just a ratio which shows how much one quantity has changed compared to other.
So, speed = distance travelled / time passed.
Let's take an example.
The distance between two places A and B is 100 metres. You took 10 seconds to reach from A to B. What was your speed?
speed = distance travelled / time passed
= 100 metres / 10 seconds
= 10 metres/second
So your speed is 10 metres/second or 10 m/s (metres per second). This means that you were covering 10 metres every 1 second.
Obviously the speed won’t be constant or the same throughout the journey. Sometimes it may be more or less than 10 m/s. So we call this the Average Speed.
Here we were just asking that okay I travelled 100 metres in 10 seconds; so how much distance did I cover in just 1 second?
Speed is generally denoted by v, distance travelled by d, and change in time or time passed by t.
So v = d / t.
