Define speed as distance travelled per unit time; recall and use the equation v = s/t

Objective

Define speed as distance travelled per unit time and remember the equation $v = \dfrac{s}{t}$.

What is Speed?

Speed tells you how fast something is moving. Think of a 🚗 car that covers 60 km in 1 hour – its speed is 60 km h⁻¹.

Speed is a scalar quantity, meaning it only has magnitude (how fast) and no direction.

The Speed Formula

Speed is calculated as:

$v = \dfrac{s}{t}$

• $v$ = speed
• $s$ = distance travelled
• $t$ = time taken

Example: A runner covers 400 m in 50 s.

$v = \dfrac{400\,\text{m}}{50\,\text{s}} = 8\,\text{m s}^{-1}$

Units of Speed

Analogy: The Speedometer

Imagine a speedometer in a car. The needle moves faster as the car goes faster. The needle’s position is the speed value – just like our formula gives the speed value.

When you press the accelerator (increase $t$), the needle moves up (increase $v$) if distance $s$ stays the same.

Exam Tip Box

When solving for speed:

1. Identify the distance ($s$) and the time ($t$).
2. Check units – convert if necessary so both are in the same system.
3. Plug into $v = \dfrac{s}{t}$ and simplify.

Remember: Speed is always positive. If the problem asks for average speed, use the total distance over total time, ignoring direction.