Forces And Braking Flashcards
What is the stopping distance?
The sum of the distance the vehicle travels during the drivers reaction time (thinking distance) and the distance it travels under the braking force (breaking distance)
How big is the stopping distance with greater speed?
Greater stopping distance
What can reaction time be affected by?
Tiredness, drugs and alcohol. Distractions may also affect.
What are the typical values of reaction time?
0.2s to 0.9s
Method for measuring reaction time
Person A and person B. Person A holds 30cm vertically - bottom end hovers over to of Person B hand.
Person A release ruler unexpectedly
Person B tries to catch ruler as soon as released
Ruler marked at the point where they caught it
This gives a measurement of the distance the ruler fell - greater distance , longer reaction time
Thinking distance
Distance travelled by a car from when a driver realize they need to brake to when they apply brakes.
What can affect the braking distance?
Adverse road and weather conditions and poor condition of the vehicle. And its speed
What are adverse weather conditions or poor car?
Wet or icy conditions. Poor condition of vehicle - breaks and tyres.
What happens when the car brakes - friction?
There is a frictional force - breaks and wheels.
Frictional force does work on the brakes - kinetic energy of car decreases and thermal energy of the brakes increases - heat up. Car decelerates.
How does the speed of the car relate to the braking force?
The grater the speed, the greater the braking force required to bring vehicle to a halt for a given distance.
Braking force does- larger deceleration will be large
Link between resultant force and acceleration.
Large deceleration- brakes overheating or loss of control.
Estimating decelerating forces
Work done by brakes when vehicle slows down =
Braking force x braking distance = 1/2 x mass x velocity squared.
What does the decelerating force equation show?
The work done is the transfer of KE. The braking distance is proportional to the speed squared.
