1. Speed and Acceleration
Physics
Speed and Acceleration

2. Distance, time and speed
To work out the speed of an object you need to know:
the distance travelled;
how long it took to travel that distance.

3. Calculating average speed
Average speed is calculated using this equation: d s x t
formula triangle
total distance
total time
average speed =

4. Speed experiment – instructions
1. Time how long it takes you to run 100m.
2. Then calculate your average speed for the run.
total distance
total time
average speed =
3. Repeat the experiment for each member of your group.
4. What was the fastest average speed for your group?

5. Speed formula triangle

6. Speed experiment – results
Name distance (m) time (s) average
speed (m/s)
100
Conclusion
The fastest member of the group with an average speed of ________ was __________.

7. Speed calculation example
A boy takes 120 seconds to travel from his home to the school, a distance of 360 m. Calculate his average speed in m/s d s x t
d (distance in m)
average speed
(in m/s)
t (time in s) =
360m
120s =
= 3 m/s
Cover the quantity to be
calculated - s (speed)

8. Speed calculation – changing units
Question 2
A group set off from home and walk at an average speed of 2.6 m/s. How far would they travel in 1 minute? d s x t
distance (m) = speed (m/s) x time (s)
= 2.6 m/s x 60s
= 156 m

9. Speed calculation and changing units
A boy takes 1 hour to travel from his home to the cinema, a distance of 10 km. Calculate his average speed in m/s. d s x t
d (distance in m)
average speed
(in m/s)
t (time in s) =
3600 s
10,000 m =
1x60x60
= m/s
Cover the quantity to be
calculated - s (speed)

10. Using the Distance, Speed, Time triangle
Moving object
Distance (m)
Time taken (s)
Speed (m/s)
Car
300
0.5
Bike 5
130
Person
1000 30
Aeroplane
12,000
2000
Cat 10
0.2
snail
1200
4.17

11. The correct answers
Moving object
Distance (m)
Time taken (s)
Speed (m/s)
Car
300
0.5
600
Bike
650 5
130
Person
1000 30
33.3
Aeroplane
12,000 6
2000
Cat 10
0.2 50
snail
1200
4.17

12. Velocity is the speed in a certain direction.
Example The velocity of a cheetah is 15 m/s east.

13. Example
What is the velocity (in m/s) of a girl who travels 1800m west from her house to her school if it takes her 10 minutes to get there?
Velocity = speed in a direction
Speed = distance / time
= 1800m/ 600s
= 3m/s
west
Answer = 3m/s west

14. Try this next one…
A dog runs 0.5km in an southerly direction. It takes her 500 seconds. What is her velocity?

15. Car graphing activity – instructions
This graphing experiment shows an animation of a car travelling along a straight road.
1. Copy the results table shown on the next slide and complete it as the movie is played.
2. Record the distance the car has travelled every five seconds.
3. Plot a graph of your results.

16. Car graphing activity – results table layout
Results table for distance/time graph
Time/seconds
Distance/metres 5 10 15 20 25 30 35 40 45 50 55

17. Car graphing activity – animation

18. Car graphing activity – results table
Results table for
distance/time graph
Time/seconds
Distance/metres 5 16 10 76 15
186 20
234 25
484 30
634 35
784 40
904 45
974 50
994 55

19. Car graphing activity – results graph

20. What distance has she travelled after 13 seconds?
How long does it take the car to travel 600m?
What is her average speed after 5 seconds?
What is her average speed after 30 seconds?

21. Car graphing activity – results graph analysis
The speed of the car is changing – the graph is not flat. The slope of the graph is less steep as the car begins
to slow down.
The car has stopped. The graph is flat – the distance of the car from the start point is not changing.
The graph is straight – there is no change in speed.
The car is going fast but at a constant speed.
The graph is straight in this part of the journey.
The car is starting to move. The curve shows that
the speed is changing. The curve is upwards as the
car accelerates at the start of the journey.

22. Acceleration is the change in velocity per unit time.
Final speed – starting speed
Time taken for the change
It is measured in m/s/s

23. Acceleration = Final speed – starting speed
A man running for a bus speeds up from 1m/s to 5m/s in 2 seconds. What is his acceleration?
Acceleration = Final speed – starting speed
Time taken for the change
= 5m/s – 1m/s 2s
= 4m/s
= 2m/s/s

24. Acceleration = Final speed – starting speed
In 10 seconds a cheetah changes her speed from 5m/s to 10m/s. What is her acceleration?
Acceleration = Final speed – starting speed
Time taken for the change
= 10m/s – 5m/s
10s
= 5m/s
= 0.5 m/s/s

25. Car graphing activity – results table layout
Time (s)
Speed (m/s) 5 10 15 20 25 30 35 40 45 50 55
Results table for speed/time graph

26. Car graphing activity – animation

27. Questions about this speed time graph..
What speed is the car travelling at after 22 seconds?
Does the speed of the car change during the drive? How can you tell this from the graph?
What is the acceleration of the car after 25 seconds?
What is the acceleration of the car between 40 and 55 seconds?

28. Question 3
The table shows the velocity of a car travelling in a particular direction on a straight road over the first ten seconds of the journey
Draw the graph
Use it to find
The velocity of the car after 7.5s
The time taken for the car to reach a velocity of 5m/s
The acceleration of the car on this journey
TIME 1 2 4 6 8 10
Velocity
1.6
3.2
4.8
6.4

29. Anagrams

30. Multiple-choice quiz