Physics

Stopping Distance is the sum of two distances.

In an emergency, e.g. Hazard in road, driver performs emergency stop, Where maximum force applied by brakes, to stop car in shortest distance.
Longer it takes, higher the risk of crashing into hazard.

Distance taken is found by:

STOPPING DISTANCE = THINKING DISTANCE + BRAKING DISTANCE

Thinking distance - how far car travels during driver's reaction time
Braking distance - distance taken to stop under braking force. (Once brakes applied)

Many Factors Affect Total Stopping Distance

Thinking distance affected by: Speed, faster, then further travel during time you take to react.
Reaction Time: longer your reaction time, longer your thinking distance. Factors which affect this are: tiredness, drugs, alcohol, distractions.

Braking Distance affected by: Speed: for a given braking force, faster vehicle travels, longer to stop.
Weather, road surface: wet,icy, leaves, oil, = less grip = less friction, between tyres & road, causing skidding.
Condition of tyres, if bald, no tread, cannot get rid of water in wet conditions, leads to skidding on top of the water.
Brakes, if worn or faulty, less force is applied = danger when needing to brake hard.

ICY CONDITIONS INCREASE CHANCES OF SKIDDING<SO INCREASE STOPPING DISTANCE, SO DRIVING TOO CLOSE IS UNSAFE. LONGER YOUR STOPPING DISTANCE, MORE SPACE NEEDED IN FRONT TO STOP SAFELY.

Reaction Times are important factor in thinking distances.

Everyone's reaction time is different. Typical reaction time is between 0.2 & 0.9s. Many different factors affect it.

Simple experiments can be done to investigate your reaction time but reaction times are short,so stopwatch is no good.
Use a computer-based test, e.g clicking a mouse when th screen changes colour.
Ruler drop test is another, longer the distance, longer the reaction time.
can calculate how long ruler falls for the reaction time because acceleration due to gravity is constant. (Roughly 9.8m/s 2.

Brakes work by friction and transferring energy away from wheels to brakes.

Brake pedal causes brake pads to be pressed onto wheels. This causes friction = work to be done.
This work transfers energy from kinetic energy stores of the wheels to thermal energy stores of the brakes. The brakes increase in temperature.
Faster a vehicle is going, more energy it has its kinetic store, so more work needed to stop it. Greater braking force needed to make it stop within certain distance.

Larger Braking force means larger deceleration. Very large decelerations can be dangerous as may cause brakes to overheat or cause vehicle to skid.

You can Estimate the Braking Force required to make vehicle decelerate & come to a stop. Typical values may need to be used.

Typical everyday speeds:
Walking - 1.5 m/s. Running - 3 m/s. Cycling - 6 m/s. Car - 25 m/s. Train - 55 m/s. Plane - 250 m/s.

How do you calculate stopping distance? STOPPING DISTANCE = THINKING DISTANCE + BRAKING DISTANCE

Name three things that will affect reaction times. Tiredness, drugs, alcahol distractions.

What is a typical reaction time? Between 0.2 and 0.9s

How can we reduce the braking distance? Better brakes

How can we reduce the thinking distance? Drinking a cup of tea

In which direction does friction act? In the opposite direction as the direction of movement