1. EXPLAINING MOTION USING FORCES
SLIDE CONTENTS
Understanding the concepts of
Speed
Average Speed
Speed Triangle
Instantaneous Speed
Graphing motions –Average speed graphs, Instantaneous speed etc
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2. Our focus is to understand how forces can explain motion.
DESCRIBING MOTION
Explain that the next two lessons cover describing motion clearly and precisely.
Our focus is to understand how forces can explain motion.

3. REVIEW AVERAGE SPEED What is average speed?
Average speed is very often defined as the total distance (in km or miles) traveled ‘d’ divided by the time ‘t’ (in sec, min, or hrs) it takes to travel that distance.
What are the units of distance and time if the unit of average speed is
Km/hr or kmph
m/hr or mph
Miles/hr or mph
Average Speed = Distance ÷ Time
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4. You Need To Know
To work out or calculate the speed of any object, you will need the following data:
The distance it has travelled
2. The time taken by the object to travel that distance.
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SPEED TRIANGLE
You will find it helpful to remember this speed triangle, when you need to make D, T or S the subject in whatever calculation you are doing. D
S × T S T
D ÷ T
D ÷ S
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6. First look at the table and calculate the answers to the missing data.
206km
2.5hr
36.6 mph
1.5hr
112 kmph
282 km
76 mph
192 miles
Average speed Distance travelled Time taken Unit
Note: Sometimes you may need to work out or calculate average speed in metres per seconds (m/s or mps). It is very important you familiarise yourself with units.
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7. To distinguish between average speed and
INSTANTANEOUS SPEED
AIM
To distinguish between average speed and
instantaneous speed

8. What is instantaneous speed?
This is the speed of an object or your speed at one instant of time or at any particular instant.
A B C D
2.5 mph mph mph
What is the instantaneous speed at AB, BC and CD?
What pattern do you see in the instantaneous speed above? Explain this pattern.
Work out the differences between average speed and instantaneous speed using
information above.

9. GRAPHING AVERAGE SPEED

10. Students analyse the motion of a sprinter in the race
ANALYSING MOTION
Students analyse the motion of a sprinter in the race