Braking And Momentum Flashcards
What is thinking distance?
The distance the vehicle travels during the driver’s reaction time
What is the braking distance?
The distance the vehicle travels once the brakes have been applied
What is stopping distance?
Thinking distance + braking distance
Does speed have a bigger effect on thinking or braking distance?
Braking distance
What is the relationship between thinking distance, braking distance and speed?
Thinking distance is proportional to speed
Braking distance is proportional to speed squared
What factors affect braking distance?
Speed
Road conditions
Conditions of brakes and tyres
Any condition that causes less friction between the tyres and road which leads to skidding
What happens when the brakes are applied?
A frictional force is applied to the wheel
Work done by the frictional force between the brakes and the wheel transfer energy from kinetic to thermal energy stores of the brakes, increasing the temperature of the brakes
Energy transfer = braking force x distance
What happens the faster a vehicle moves or the greater it’s mass?
The greater amount of energy in its kinetic energy store
The more work that has to be done to transfer the energy to slow down
The greater the braking force needed to stop it in a certain distance
The greater the distance needed to stop it with a certain braking force
What is reaction time?
Ranges from 0.2 to 0.9s
Affected by tiredness, drugs, alcohol, distractions
How can you measure reaction time?
Ruler drop test
Computer
What is deceleration?
Braking force = mass x acceleration
The greater the braking force, the greater the deceleration
If the braking force is too large, the brakes may overheat or the car may skid, causing the driver to lose control
How do you calculate change in momentum?
F = ma
a = change in v/ t
F = m x change in v/ t
The greater the time taken for the change in momentum…
The smaller the rate of change
The smaller the force
Force acting on an object = rate of change in momentum of an object
How do vehicle safety features increase time taken for change in momentum?
Air bags
Cycling helmets
Crash mats
