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Acceleration

Non-uniform Motion means that the object is going sometimes slow at other times fast. It therefore has to slow down and speed up. In order to do so the car ort bike has to accelerate, that does not mean anything else but go slower or faster over a certain time interval. Non-uniform motion therefore involves acceleration.

It is very important to understand what acceleration really is and how to calculate it. In order for acceleration to occur the object has to change its speed. Therefore change in speed is important. The second quantity that matters wile become clear when you remember how the acceleration of a car is given in a brochure or an ad. The car is said to accelerate from 0 to 60 in such an amount of time. Inn your workbook several examples are given. Which car do you think has the greatest acceleration? Right, the one with that can reach 60 mph in the smallest amount of time. So the second quantity necessary to calculate acceleration is the amount of time in which this change of speed occurs. Therefore the definition of acceleration is acc .

Look at the picture to the right. It is impossible to say which  has the larger acceleration.

Note that you can change your speed quite dramatically even if your speed is slow. Imagine a kid on a small bike with training wheels. We would agree that this kid is not going very fast. Now let’s imagine the same kid missing a turn and hitting a wall (a necessary sacrifice in the name of science). The speed changed from slow to zero. Now imagine a fast car coming to a stop - gently. The change in speed will be much greater from, say, 70 mph to 0. But what did I mean by “gently”? I meant that it will necessary to take a very large amount of time for this car to come to a stop. So the change in speed is great but so is the change in time. The ratio is what is important and it might well be that the little kid on the bike had the greater acceleration – because the amount of time this change happened in was very small.

Since acceleration involves the chnage in time it is impossible to tell from a photo which object has the larger acceleration at the instant shown. It is possible to tell which object can achieve the largest acceleration but not which one does the instant they are shown. Look at the picture to the right. It is impossible to say which  has the larger acceleration.

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One of the fastest cars the McLaren F1 can go up to 240 mph. This does not mean that it also accelerates quickly, but this one does. From 0 to 60 mph in under3 secnds. During a crash where a McLaren F1 hit a tree parts of the car were reportedly found 400 meters away from the crash site.

 

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