- Define and explain Speed and Velocity in your own words
- Use key terms such as speed accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
Describing motion precisely is the first step to predicting it. With a few equations and some clever graphs, you can work out how fast anything moves — from a sprinter to a satellite. This chapter turns journeys into numbers.
This lesson focuses on Speed and Velocity: calculating speed from distance and time, and seeing how velocity adds direction.
Calculating speed from distance and time, and seeing how velocity adds direction.
Key ideas
Speed tells you how fast, velocity tells you how fast and where to
Speed = distance ÷ time is a scalar with no direction. Velocity adds direction, making it a vector. Two cars can share a speed of 20 m/s yet have different velocities if they head opposite ways — and that difference matters in collisions.
Graphs turn journeys into pictures
On a distance–time graph, the gradient (slope) equals the speed — steeper means faster, flat means stationary. On a velocity–time graph the gradient gives acceleration, and the area under the line gives the distance travelled. One graph can replace a whole table of data.
Key term — speed: How fast something moves: distance travelled divided by time taken, measured in m/s or km/h.
How is distance found from a velocity–time graph?
It equals the area under the graph, between the line and the time axis.
Answer: It equals the area under the graph, between the line and the time axis.
- Reading the gradient of a velocity–time graph as speed The gradient of a velocity–time graph is acceleration; speed is read straight off the vertical axis.
- Mixing up distance and displacement Distance is the total path travelled; displacement is the straight line from start to end — they match only on a straight one-way trip.
Practice
Yes — its direction is changing, so its velocity is changing, which means it is accelerating even though its speed is constant.
The object is stationary — distance is not changing as time passes.
100 ÷ 12.5 = 8 m/s.
25 × 40 = 1000 m.
Quick check
Which of these best defines "speed"?
A van accelerates from 10 m/s to 22 m/s in 6 s. Find the acceleration.
- Speed and Velocity: calculating speed from distance and time, and seeing how velocity adds direction.
- Speed tells you how fast, velocity tells you how fast and where to: Speed = distance ÷ time is a scalar with no direction.
- velocity: Speed in a stated direction — a vector, so 30 m/s north and 30 m/s south are different velocities.
- Watch out for: reading the gradient of a velocity–time graph as speed