Kinematics

Speed, velocity, acceleration and motion graphs for travel in one direction.

SEC G3 Combined Science Physics component 2027
3 lessons

Before you begin

Kinematics describes how things move: how fast, in which direction and how quickly their speed changes. The lessons start with speed, velocity and acceleration, then plot and read distance–time and speed–time graphs. They finish with free fall and with choosing the right method for a whole motion problem.

Be comfortable with: SI units and prefixes, because speeds and times are often given in km/h or minutes.

Learning goals

State what speed means
State what velocity means, including its direction
Calculate average speed from total distance and total time
Calculate acceleration as change in velocity divided by time taken
State what uniform acceleration means
Interpret examples of non-uniform acceleration
Plot and interpret a distance–time graph
Plot and interpret a speed–time graph for one-direction motion
Deduce rest, uniform speed and non-uniform speed from a distance–time graph
Deduce rest, uniform speed and uniform or non-uniform acceleration from a speed–time graph
Use area under a speed–time graph to determine distance travelled
Recall constant free-fall acceleration near Earth as approximately 10 m/s²

Syllabus statements covered

state what is meant by speed and velocity
calculate average speed = distance travelled / time taken
state what is meant by uniform acceleration and calculate the value of acceleration using change in velocity / time taken
interpret given examples of non-uniform acceleration
plot and interpret a distance-time graph and a speed-time graph for motion in one direction
deduce from the shape of a distance-time graph when a body travelling in one direction is: (i) at rest (ii) moving with uniform speed (iii) moving with non-uniform speed
deduce from the shape of a speed-time graph when a body travelling in one direction is: (i) at rest (ii) moving with uniform speed (iii) moving with uniform acceleration (iv) moving with non-uniform acceleration
calculate the area under a speed-time graph to determine the distance travelled for motion in one direction with uniform speed or uniform acceleration
state that the acceleration of free fall for a body near to the Earth is constant and is approximately 10 m/s²

Lessons

Work through them in order.

Practise and check

Topic reference

Quick reference

Quantity	Relationship	Unit
average speed	average speed = distance travelled ÷ time taken	m/s
acceleration	acceleration = change in velocity ÷ time taken	m/s²
free fall	acceleration of about 10 m/s², downwards	m/s²

Graph	Gradient	Area under the line	Flat line
distance–time	speed	—	at rest
speed–time	acceleration	distance travelled	uniform speed

Core knowledge to remember

Speed is the distance travelled per unit time. Velocity is speed in a stated direction.
Uniform acceleration means the velocity changes by the same amount in each second.
On a distance–time graph, a horizontal line shows a body at rest, a straight sloping line shows uniform speed and a curve shows non-uniform speed.
On a speed–time graph, a horizontal line shows uniform speed, a straight sloping line shows uniform acceleration and a curve shows non-uniform acceleration.
The acceleration of free fall for a body near to the Earth is constant and is approximately 10 m/s².

Common mistakes

Finding average speed by averaging two speeds instead of dividing the total distance by the total time.
Subtracting the velocities the wrong way round when calculating acceleration.
Reading a speed–time graph as if it were a distance–time graph.
Forgetting to change minutes to seconds, or km/h to m/s, before calculating.