P2 Unit 2.4 On the road

Lesson 3: On the road

Textbook section P2 2.4

Aim: What factors affect the stopping distance of vehicle on the road?

Starter 10 min: 10 key questions that provide a recap of the previous two lessons. These should be attempted without books. Mr C will provide the answers and students should self assess their work.

Main activity 30 min:
When a vehicle is travelling at a steady speed the resultant force acting on it is zero, so driving forces are equal & opposite to frictional forces.
The braking force needed to stop that vehicle depends on the velocity and mass of the vehicle. > velocity and/or > mass = > braking force.
The total stopping distance of a vehicle is the distance it travels during the driver’s reaction time (the thinking distance) plus the distance it travels under the braking force (the braking distance).
Stopping distance = thinking distance + braking distance. With the same driver and car the thinking & braking distance will increase when the initial velocity increases.
The thinking distance will increase if the driver is tired or under the influence.
The braking distance can be increased by poorly maintained roads, bad weather conditions & the condition of the car i.e. worn brakes or tyres.

Students have to...
1. Use the textbook to draw a diagram or series of diagrams that summarise the above, it should be simple and concise and include as many key points as possible. To help them begin a diagram of Mr Average in his average car is shown on the board.
What is a stopping distance? Explained by Mr Average.
What factors affect braking force?
What factors affect the thinking distance and braking distance?
2. Complete summary questions 1 & 2 on pg 203 of the text book. Mr C will provide answers at the end of the lesson.
3. If there is time the lesson can be finished with some reaction tests using software on the computer.

http://www.gcse.com/fm/stopping_distances.htm a good summary of the material covered in this lesson.

Plenary (10 min)...
Students can try some practice exam questions. Mr C will give the answers and students should mark and correct their own work.

AQA Specification – Physics 2.13.2
· When a vehicle travels at a steady speed the frictional forces balance the driving forces.
· The greater the speed of a vehicle the greater the braking force needed to stop it in a certain distance.
· The stopping distance of a vehicle depends on the distance the vehicle travels during the drivers reaction time and the distance it travels under the braking force.
· A driver’s reaction time can be affected by tiredness, drugs and alcohol.
· A vehicle’s braking distance can be affected by adverse road and weather conditions and poor condition of the vehicle.