Physics (5054)
Average speed is the total distance divided by total time for a whole journey Instantaneous speed is how fast you're going at one exact moment (like what your speedometer shows)
A straight diagonal line = constant speed A steeper line = faster speed A flat horizontal line = stationary (not moving) A curved line = changing speed (acceleration or deceleration)
The area under the graph = distance travelled A horizontal line = constant speed A line going up = acceleration A line going down = deceleration
Topic 1 of 8Cambridge O Levels
Speed, Distance & Time
Understanding motion through everyday examples
Speed tells us how fast something is moving. It's calculated by dividing the distance travelled by the time taken.
Formula: Speed = Distance / Time (v = d/t)
Units: Speed is measured in metres per second (m/s) or kilometres per hour (km/h).
Average Speed vs Instantaneous Speed:
Distance-Time Graphs:
Speed-Time Graphs:
Key Points to Remember
- 1Speed = Distance / Time (v = d/t)
- 2SI unit of speed is metres per second (m/s)
- 3On a distance-time graph, the gradient gives speed
- 4On a speed-time graph, the area under the curve gives distance
Pakistan Example
Karachi to Lahore on the Motorway
The M-2 Motorway from Lahore to Islamabad is about 375 km. If a bus takes 5 hours to complete this journey, its average speed is 375/5 = 75 km/h. But the bus doesn't travel at exactly 75 km/h the whole time — it speeds up, slows down at toll plazas, and sometimes goes faster on empty stretches. The speedometer shows instantaneous speed, while 75 km/h is the average speed.