1. Speed-Time Graphs

2. Interpreting Velocity/time graphs
the gradient of a velocity/t graph is the acceleration t v
Constant velocity (the velocity remains the same)

3. Interpreting Velocity/time graphs
Faster constant acceleration
Slow constant acceleration
Constant acceleration (the velocity changes at a constant rate)

4. Interpreting Velocity/time graphs
decreasing acceleration
Increasing acceleration
Changing acceleration (the rate of change in velocity per second changes)

5. Interpreting Velocity/time graphsB C D
RC Car Journey
A -fast acceleration (steep gradient and line straight)
B –slower acceleration (shallow gradient and line straight)
C –constant velocity (line horizontal)
D –Very fast deceleration (steep gradient, straight line, sloping down)

6. Acceleration
An object changing its speed is said to be accelerating. If the acceleration is:
positive (eg. 2ms-2) = object speeding up
negative (eg. -2ms-2) = object slowing down or decelerating

7. Acceleration (change in speed)
acceleration is a measure of how quickly the velocity (speed) of an object is changing
If the object is a constant acceleration (unbalanced forces) the formula is;
The units for acceleration are ms-2
Note; v =final velocity-initial velocity
v=vf - vi

8. Example
A racing car speeds up from 8ms-1 to 24ms-1 and takes 8 s to do so. Calculate the acceleration.
= 24 – 8 = 16ms-1
A = 16ms-1 8s
= 2ms-2

9. Examples
A cyclist starts from rest and accelerates to 15ms-1 in 8s. Calculate her acceleration ms-2
A runner jogging at 2.5ms-1 increases his pace to 4.5ms-1 in 3s. What was her acceleration? ms-2

10. Calculating the Gradient (v/t graphs)
the gradient of a velocity/time graph is the acceleration
For the green line;
Gradient=Rise/Run
=(14-2)/12
=1.0 ms-2
For the blue line;
Gradient=Rise/Run
=6/12
=0.5 ms-2
For the red line;
Gradient=Rise/Run
=24/12
=2.0 ms-2

11. Velocity/time graphs
The area under the graph is the distance travelled (as the cut up ticker timer tape showed)
Area of triangle=½base ×height = ½×6×9 =27m
Area of rectangle=base × height = 4× =36m
Total area=27+36=63m

12. Worksheet