1. OBJECTS IN MOTION.
02. Speed and velocity.
Ian Anderson
Saint Ignatius College Geelong

2. DO YOU REMEMBER?
Distance is a measure of how far an object travels
over a certain period of time.
 For example if you drove from Geelong to Sydney, your
distance travelled would be 940 km.
 When you return to Geelong, your total distance
travelled would be 1860 km.

3. DO YOU REMEMBER?
Displacement however describes the change in
position of an object and its direction over a certain
period of time.
 For example if you drove from Geelong to Sydney, your
displacement would be 940 km N.
 When you return to Geelong, your displacement would
be 0.

4. WHAT IS SPEED?
Speed is a measure of how fast a moving object is
travelling.
Speed is the rate at which distance is covered.
Speed is measured in SI units of metres per second
(m/s or ms-1).
 For cars you will often find it measured in kilometres
per hour (km/h or kmh-1).
Speed is a scalar quantity because it only has size
and no direction.

5. WHAT IS SPEED?
The speedo on a car measures instantaneous
speed.
Instantaneous speed is the speed at any moment in time.
More often we talk about average speed.
Average speed is the total distance covered by an object
per given time period.

6. CALCULATING SPEED.
Average speed = total distance covered per given
time period.
Average speed =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑖𝑚𝑒
𝑠 𝑎𝑣 =
𝑑
𝑡

7. WHAT IS VELOCITY?
Velocity is speed in a given direction.
Velocity is the rate at which distance is covered in a
given direction.
Velocity has the same SI units as speed (m/s or
ms-1), with the same direction as the displacement.
Velocity is a vector quantity because it has both size
and direction.

8. Average velocity = total distance and direction
covered per given time period.
Average velocity =
𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
𝑡𝑖𝑚𝑒
𝑣 𝑎𝑣 =
𝑑
𝑡
CALCULATING VELOCITY.

9. POSITION-TIME GRAPHS.
 Position-time graphs (also called displacement-time
graphs) show the total distance travelled by an
object over time.
 Position-time graphs can be used to determine
 The displacement of an object at any point in time.
 The speed or velocity of an object at any point in time.

10. POSITION-TIME GRAPHS.
 Position-time graphs (also called displacement-time
graphs) show the total distance travelled by an
object over time.
 Position-time graphs can be used to determine
 The displacement of an object at any point in time.
 The speed or velocity of an object at any point in time.

11. POSITION-TIME GRAPHS.
The gradient of a position-time
graph gives you speed of the
object.
 A steep position-time graph
indicates a faster speed than a
graph with a lesser slope.
 A horizontal position-time graph
indicates that the object is at
rest.
Source: Rickard et al. (2006)

12. POSITION-TIME GRAPHS.
To calculate the average
speed using a position-
time graph, you need to
calculate the gradient of
the slope formed by the
line joining the position of
your initial position with
the final position.
Source: Sharwood et al. (2006)

13. POSITION-TIME GRAPHS.
Use the position-time graph to answer the questions
following.
Source: Sharwood et al. (2006)

14. POSITION-TIME GRAPHS.
1. At what time/s was
the object stationary?
Answer =
 Between 0 & 30 s and
again between 60 &
80 s.
Source: Sharwood et al. (2006)

15. POSITION-TIME GRAPHS.
2. What was the objects
distance from it’s
starting point at
t=60 s?
Answer =
 60 m
Note: At 60 s the object’s
displacement is -20 m
from point (P). Source: Sharwood et al. (2006)

16. POSITION-TIME GRAPHS.
3. What was the objects
displacement from it’s
starting point at t= 60
s?
Answer =
 60 m S
Source: Sharwood et al. (2006)

17. POSITION-TIME GRAPHS.
4. What was the objects
average speed
between 80 and 100
s?
Answer =
Sav = 1 m/s
Source: Sharwood et al. (2006)

18. POSITION-TIME GRAPHS.
5. What was the objects
average velocity
between 80 and 100
s?
Answer =
Sav = 1 m/s N
Source: Sharwood et al. (2006)

19. BIBLIOGRAPHY.
Rickard, G., Phillips, G., Ellis, J., Jeffery, F., &
Roberson, P. (2006). Science Dimensions 4:
Coursebook. Melbourne: Pearson Education
Australia.
Sharwood, J. (Ed.). (2006). Science Edge 4.
Melbourne: Thomson Learning.

20. http://SICkScience10.wikispaces.com/