Speed, Distance and Time

This lesson covers the speed equation, distance–time graphs and typical speeds, as required by the Edexcel GCSE Combined Science specification (1SC0). Speed is one of the most fundamental ideas in physics and underpins your understanding of motion.

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The Speed Equation

Speed is the distance travelled per unit time. It is a scalar quantity.

$\text{speed} = \frac{\text{distance}}{\text{time}}$speed=timedistance​

$v = \frac{d}{t}$v=td​

where:

• v = speed (m/s)
• d = distance (m)
• t = time (s)

This can be rearranged:

$d = v \times t$d=v×t

$t = \frac{d}{v}$t=vd​

Exam Tip: Use the formula triangle to rearrange: cover the quantity you want to find. d is on top, v and t are on the bottom. If side by side, multiply; if one is above the other, divide.

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Worked Examples

Example 1: A cyclist travels 600 m in 40 s. What is her speed?

$v = \frac{d}{t} = \frac{600}{40} = 15 \text{ m/s}$v=td​=40600​=15 m/s

Example 2: A car travels at 25 m/s for 120 s. How far does it go?

$d = v \times t = 25 \times 120 = 3000 \text{ m}$d=v×t=25×120=3000 m