Physics A Level | Chapter 2: Accelerated motion 2.1 The meaning of acceleration
QUICK OFF THE MARK
The cheetah (Figure 2.1) has a maximum speed of more than $30\,m\,\,{s^{ - 1}}$ ($108 km/h$). A cheetah can reach $20\,m\,\,{s^{ - 1}}$ from a standing start in just three or four strides, taking only two seconds.
A car cannot increase its speed as rapidly but on a long straight road it can easily travel faster than a cheetah.
How do you think such measurements can be made? What apparatus is needed?
In everyday language, the term accelerating means ‘speeding up’. Anything whose speed is increasing is accelerating. Anything whose speed is decreasing is decelerating.
To be more precise in our definition of acceleration, we should think of it as changing velocity. Any object whose speed is changing or which is changing its direction has acceleration. Because acceleration is linked to velocity in this way, it follows that it is a vector quantity.
Some examples of objects accelerating are shown in Figure 2.2.
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