Stopping Distances Flashcards
All 17 cards in this deck
What are the steps of the ruler drop test for measuring reaction time?
e.g. a ruler is dropped between a partner's open fingers
- Hold the ruler vertically with the zero mark between your partner's open thumb and finger.
- Release it without warning; your partner catches it as quickly as possible.
- Read the distance fallen and convert it to a time; repeat and take a mean.
What is a typical human reaction time?
About 0.2–0.9 s.
Describe a computer-based method of measuring reaction time.
The person clicks a mouse or presses a key as soon as an image or sound is produced, and the computer times the delay between stimulus and response.
True or false? In the ruler drop test, a greater distance fallen means a shorter reaction time.
False. A greater distance fallen means a longer reaction time.
What two distances make up the stopping distance of a vehicle?
Stopping distance = thinking distance + braking distance.
What is the thinking distance?
The distance travelled by the vehicle during the driver's reaction time, before the brakes are applied.
What is the braking distance?
The distance travelled by the vehicle from the brakes being applied until it stops.
True or false? If a car's speed doubles, its braking distance also doubles.
False. Braking distance is proportional to speed squared (), so it becomes about four times greater.
Name four things that increase a driver's reaction time.
Drugs, alcohol, tiredness and distractions (e.g. using a phone).
How does a greater vehicle mass affect stopping distance?
A greater mass gives a longer braking distance, so the stopping distance increases.
How do worn brakes affect stopping distance?
Worn brakes give a smaller braking force, so the braking distance and stopping distance increase.
Why is it safer to drive more slowly on a wet road?
A wet road means less friction between the tyres and the road, so stopping distance is increased; a slower speed gives a shorter braking distance and reduces the chance of skidding.
Why are large decelerations dangerous for people in a vehicle?
A large change in velocity in a short time means a large force acts on the occupants (), which can cause serious injury.
What typical mass is used for a car when estimating the forces involved in braking or a collision?
About 1000 kg.
How does a driver's reaction time on a real road compare with a reaction time measured in a lab test such as the ruler drop?
It is usually longer, typically up to about 1 s for an alert driver, and longer still if the driver is tired or distracted.
In the ruler drop test, why can the distance the ruler falls be turned into a reaction time?
The ruler falls from rest with a constant acceleration (g, about 10 m/s²), so each distance fallen matches one particular time.
What two factors affect a vehicle's thinking distance?
The driver's reaction time and the vehicle's speed; increasing either one increases the thinking distance.