Lesson+5+Acceleration+Starter

Look at the two cars that are shown on the screen. Both cars are at rest to start with and then speed up to 100 km/hour.

[object Object],[object Object],because speed change is the same for both cars no accelerating Can you tell from the information given which car has the greater acceleration? Explain. Which car would you expect to have the greater acceleration? Suggest reasons. the sports car more streamlined/less air-resistance lighter but still powerful engine (higher power to weight ratio) etc

[object Object],[object Object],[object Object],[object Object],[object Object],rate The sports car would change speed in a shorter time . We need to measure the time taken for the speed change. So acceleration actually measures the __________ of change of speed/velocity.

Suppose the times taken for the two cars are: second So acceleration means the change in speed per ________. Acceleration is rate of speed change Acceleration is rate of speed change 10 B 5 A Time taken to reach 100 km/hour (s) Car

[object Object],[object Object],final speed – initial speed time change in speed time

Calculating Acceleration ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],kilometres per hour per second 20 ___________? 5 100 - 0 20 km/h/s 100 - 0 10 10 km/h/s

[object Object],[object Object],m/s ? So we need to convert the cars’ speeds to m/s 100 km/h = 100 000 m/s 3 600 = 28 m/s = approx 30 m/s So the acceleration in SI units is:

Car A ,[object Object],Metres per second acceleration = 30 - 0 5 acceleration = 6______________ 6 metres per second squared 6 m/s/s Or acceleration = 6 m/s 2 We say:

Car B acceleration = 30 - 0 10 acceleration = 3 m/s/s acceleration = 3 m/s 2

To write a general equation we use these symbols: acceleration = a final velocity = v time = t initial velocity = u ,[object Object],[object Object],[object Object],Rearranging for t: t = v - u a

To write a general equation we use these symbols: acceleration = a final velocity = v time = t initial velocity = u ,[object Object],[object Object],Rearranging for v: v = u + at

To write a general equation we use these symbols: acceleration = a final velocity = v time = t initial velocity = u ,[object Object],[object Object]

Lesson+5+Acceleration+Starter

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