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Introduction 5
Fig. 1.4 Linearity: more handwheel input results in proportionally more yaw
rate (vehicle on left)
2
1
3
Fig. 1.5 A thought experiment comparing centripetal acceleration with linear
acceleration
acceleration – ‘centre seeking’. Note that speed is not the same as velocity;
travelling in a curved path with a constant speed implies a changing direction
and therefore a changing velocity. The centripetal acceleration definition
causes some problems since everyone ‘knows’ that they are flung to
the outside of a car if unrestrained and so there is much lax talk of centrifugal
forces – ‘centre fleeing’. To clarify this issue, a brief thought experiment
is required (Figure 1.5). Imagine a bucket of water on a rope being
swung around by a subject. If the subject looks at the bucket then the water
is apparently pressed into the bucket by the mythical ‘centrifugal force’
(presuming the bucket is being swung fast enough). If the swinging is
halted and the bucket simply suspended by the rope then the water is held
in the bucket by the downward gravitational field of the earth – the weight
of the water pulls it into the bucket. Imagine now a different scenario
in which the bucket (on a frictionless plane) is pulled horizontally towards
the observer at a constant acceleration in a linear fashion. It’s best not to