Lesson 1: Skids and friction

Investigating the force of friction.

Learning objectives

For students to:

  • understand that it can be difficult for drivers to stop in time if a pedestrian steps out into the road
  • investigate the force of friction and relate it to road surface and conditions
  • relate results to skids or stopping distances of cars.

Resources

Curriculum

Links to Science -1a, 1b, 2a, 2b, 2c, 2d, 3c

Time

1 hour


Introduction

  • Tell students that you are going to be looking at friction.

Stopping distances - 15 minutes

  • Ask students what might make it difficult for a driver to stop for you if you step out into the road. (If they don't notice you because they are distracted, if they can't stop in time.)
  • Focus on distraction first. Deliver either the "What impact does distraction have" or "Driver distraction introduction" section of the PSHE and Citizenship Distraction action lesson plan.
  • Now ask what else can affect stopping distances. (The weight of the car, the road surface, the weather, the tyre tread, speed.) Describe the role that friction plays in making the car stop.

Stopping distances and friction - 20 minutes

  • Use an empty margarine tub or similar is used to represent a car, securing weights or plasticine in the tub to give it greater mass. The tub is launched with a constant initial push and the distance it travels across a surface is measured. This represents a vehicle's stopping distance.
  • A launcher can be improvised by stretching an elastic band between two legs of a stool. The elastic band is pulled back before the vehicle is 'loaded' and released. Using a force meter to pull the elastic band back set distances allows the force of the launcher to be estimated. A datalogger can be used to get a readout of the vehicle's motion and deceleration.
  • Increasing the force of the initial push could be used to investigate the stopping distance with different initial speeds.

Friction, losing grip and skidding - 20 minutes

  • To investigate skidding when friction is overcome, the car is pulled using a force meter. The force required to start the tub sliding is noted. This is equivalent to the vehicle's wheels locking and skidding.
  • For both scenarios, a range of surfaces could be tested:
    • Tile
    • Wood
    • Carpet
    • Concrete
    • Wet and dry conditions
    • Abrasive paper, to simulate Shellgrip (the 'grippy' coating applied to certain roads, for example, at pedestrian crossings)
    • Sand or grit to represent debris on the road surface

Plenary - 5 minutes

  • Ask students to think about what they discussed at the start of the lesson. What have they learnt from conducting the experiment? Will this affect their behaviour as a pedestrian?