01Why this matters
Travel planning uses average speed, while motion analysis often needs velocity because direction matters.
02See it
03Understand it
Average speed is total distance divided by elapsed time. Average velocity is displacement divided by elapsed time.
Speed is a scalar and cannot be negative. Velocity is a vector and can have a negative component along a chosen axis. An average summarises a whole interval; it does not tell you the speed at every instant. Use matching distance and time units before dividing.
04Guided example
A cyclist covers 600 m in 120 s. Find average speed.
- Use the total distance 600 m and total elapsed time 120 s, including any stops.
- Divide: average speed = 600/120 = 5 m/s.
- Convert if useful: 5 × 3.6 = 18 km/h.
05Try it
06Practise it
07Use it in the real world
A 60 km journey taking 1.5 h has average speed 40 km/h, even if the vehicle sometimes travels faster and sometimes stops.
Go a little deeper
Instantaneous velocity is the rate of change of position at an instant. It corresponds to the gradient of a tangent on a position-time graph.
08Quick check
09Summary
Average speed is total distance divided by elapsed time. Average velocity is displacement divided by elapsed time. Convert if useful: 5 × 3.6 = 18 km/h.
Before moving on, explain the worked example in your own words. Use the hint on any question you want to revisit.
10Key idea
average speed = distance / time
Distance in m and time in s give speed in m/s. Time must be positive.
distance = average speed × time
Find this in the formula library →