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Mechanics Speed, Acceleration and Car Safety
Speed Speed is a measure of how fast an object is travelling. We say: The S.I unit for Speed is m/s or ms
Acceleration This refers to an increase in speed, or if the speed decreases, we talk about deceleration. The S.I units for acceleration are m/s/s which can be written as m/s
Speed-Time graphs These refer to the acceleration of an object and are very similar to distance-time graphs : so you to need look at the axes of the graphs very carefully. Speed and Acceleration Since the area under a speed-time graph is: on cancelling time in this equation, we get : AREA under the graph = distance travelled
Practical Work : To find the average speed of a 'car' on a ramp Apparatus : ramp, 'car', stopwatch, metre ruler. Method Measure the distance **d**between A and B, which are the start and stop points on the ramp (make**d**about one metre).When the front wheels of the 'car' are on mark A, let the car go (DO NOT PUSH IT) Start timing and then stop the stopwatch when the front wheels pass mark B Repeat this procedure at least twice more to find the average time taken to move distance **d**Calculate the average speed for this distance:
Change the height of the ramp above the table. Keeping the distance
Questions Is this average speed the same as before? Explain your answer. Is the average speed, the same as the constant speed of the car? Explain your answer.
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