Stopping Distances

Stopping Distances 🚗

When a hazard appears, a car cannot stop instantly. First the driver has to react, and then the brakes have to do their work. The total distance covered from spotting the danger to stopping still is the **stopping distance** — and it is bigger than most people think.

Thinking + braking 🛑

The stopping distance is made of two parts: **stopping distance = thinking distance + braking distance** **Thinking distance** is how far the car travels during the driver's **reaction time**, before the brakes come on. **Braking distance** is how far it travels while the **brakes** bring it to a stop.

Total stopping distance

An interactive activity.

Thinking distance 💭

**Thinking distance** depends on the driver's **reaction time** and the car's **speed**. Reaction time is made longer by **tiredness, alcohol, drugs and distractions** (such as a phone). And because a faster car covers more ground in the same reaction time, thinking distance also grows with **speed**.

Braking distance 🛞

**Braking distance** depends on the **speed**, the **mass** of the vehicle, the **road and weather conditions** (wet or icy roads are worse) and the condition of the **brakes and tyres**. Crucially, braking distance grows with **speed squared** — so **doubling the speed roughly quadruples the braking distance**.

What lengthens braking distance?

Select ALL THREE things that increase the BRAKING distance (not the thinking distance).

• Driving faster
• A wet or icy road
• Worn brakes or tyres
• The driver being tired
• The driver checking their phone
• A dry, grippy road

Double the speed

Braking distance depends on the speed squared. If a car doubles its speed, roughly what happens to its braking distance?

• It increases about four times
• It simply doubles
• It stays the same
• It halves

A tired driver, a wet road

An interactive activity.

The braking force 🔥

**(Higher tier)** To stop in a given distance, the brakes must apply a **braking force**. A greater force causes a greater **deceleration** — from **F = m a**. At high speed, the force and deceleration needed to stop quickly can be very large (and dangerous). The brakes do work, transferring the car's **kinetic energy** to **thermal energy**, so they heat up.

Find the braking force

An interactive activity.

Match each term to its meaning

Stopping summary

Stopping distance = thinking distance + _____ distance. Thinking distance is increased by tiredness, alcohol and _____. Braking distance is increased by poor road conditions and worn brakes, and grows with speed _____. The brakes transfer the car's kinetic energy to _____ energy.