5.8.2 Stopping Distance

Vehicle Stopping Distances

After seeing a hazard:
- Thinking Distance:
- This is how far the car goes before you react. It's the distance you travel while your brain is deciding to hit the brakes.
- Braking Distance:
- This is how far the car travels after you hit the brakes, while the car is slowing down until it comes to a stop.

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Formula

\text{stopping distance} = \text{thinking distance} + \text{braking distance}

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The greater the speed, the greater the distance travelled during the same time (reaction time).

Reaction times vary (0.2 – 0.9s for each person).
- Measure reaction times by the "ruler drop":

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Drop a ruler through the person's open hand, the time it takes to catch it can be determined by

s = ut + \frac{1}{2}at^2\ where \ u = 0 \ and\ a=g,\ so \ t = \sqrt{2gs}

Where s is the distance the ruler travels through the hand

When a force is applied to the brakes of a vehicle:
- Work is done by the brakes (by friction) onto the wheel.
- So the vehicle's kinetic energy reduces.
- And the temperature of the brakes increases.
Greater speed = greater braking force needed to stop the car (over the same distance).
- So greater force = greater acceleration.
- This may lead to brakes overheating and a loss of control, which is dangerous.