Cambridge VIII - PHYSICS

1. 9.1 Speed
Physics VIII Cambridge
Sir. Muhammad Abdul Mageid

2. Learning outcomes
After this topic you should be able to :
- Use the speed equation to calculate the speed of a range of objects
- Measure the average speed of an object
- Make predictions using scientific knowledge and understanding
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3. What is meant by
The speed of sound through air = 340 m/s
This means that sound travels a distance
of 340 metres each second
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4. 1.
Definition of speed
4

5. “Speed: is the distance travelled
in unit time .
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6. 2.
Speed Calculations
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7. SPEED EQUATION
◈ During a journey an object can travel at different
speeds.
◈ The average speed for the journey can be
calculated using the total distance travelled and
the duration of the journey
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8. “Average Speed: is the total
distance travelled divided by
the total time .
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9. Speed Equation
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑
𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛
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10. 10

11. 3.
Speed Units
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12. DIFFERENT SETS OF UNITS FOR THE SPEED
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Distance unit Time unit Speed unit
Metres (m) Seconds (s) Metres per second (m/s)
Kilometres (km) Hours (h) Kilometres per hour (km/h)

13. Example calculations
Example 1
A runner travels a distance of 400 m in 80 s
𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝒔𝒑𝒆𝒆𝒅 =
𝒅
𝒕
=
𝟒𝟎𝟎
𝟖𝟎
= 𝟓. 𝟎 𝒎/𝒔
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14. Example calculations
Example 2
A train travels a distance of 40 km in 2 h. The average speed of the train is
found using the equation
𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝒔𝒑𝒆𝒆𝒅 =
𝒅
𝒕
=
𝟒𝟎 𝒌𝒎
𝟐 𝒉
= 𝟐𝟎 𝒌𝒎/𝒉
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15. QUESTIONS
1. Complete this table to calculate the speed of the objects
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Object Distance travelled Time taken Average speed
Bus 60 km 2 h
Athlete 400 m 50 s
Passenger
plane
2000 km 8.5 h
Racehorse 1800 m 120 s
Shark 1000 m 100 s
Snail 4 m 100 s

16. QUESTIONS
2. The table of data shows some world records for the 800 m race.
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Runner Year Time /s
Dave Wottle 1972 104.3
Alberto Juantorena 1976 103.5
Sebastian Core 1977 102.4
Wilson Kipketer 1997 101.1
David Rudisha 2012 100.9
a) Calculate the average speed
for each of the runners
b) Plot a graph to show how
the average speed has
increased from 1972 to 2012

17. THANKS!
Any questions?