Speed
Simple Explanation
Speed measures how fast an object is moving — the distance it covers in a given time, regardless of direction.
Why Do We Need It?
Speed is the simplest, most everyday measure of motion — from a car's speedometer to how fast you can run.
Formula
Speed
speed = distance / time
How fast an object is moving, regardless of direction.
- speed
- — rate of motion, in metres per second (m/s)
- distance
- — total path length travelled, in metres (m)
- time
- — time taken, in seconds (s)
When to use it: Whenever you need how fast something moved, without needing to know its direction.
Worked Example
Calculate a cyclist's speed
A cyclist covers 150 m in 30 s. What is their speed?
Why Does This Work?
Dividing the total distance covered by the time it took gives exactly how much distance is covered, on average, for each second — the definition of speed.
Real-Life Example
Reading a speedometer
A car's speedometer shows how fast the car is travelling at any instant.
It is continuously calculating (an instantaneous version of) distance covered per unit time — exactly this formula.
Practice
A runner covers 100 m in 20 s. What is their speed?
EasyCommon mistake
Forgetting to keep units consistent — mixing kilometres and seconds, for example, without converting, gives a meaningless number.
Quick Review
- speed = distance / time
- Speed is a scalar — it has no direction.
- Common units: m/s or km/h.