Friction 01 January 2019 Objectives: To describe the causes and effects of frictional forces. Explain how a lubricant to reduce frictional forces.

Starter (5 mins) Show the students a car performing a race lap and creating skid marks Ask the students to explain how and why skid marks were produced. http://www.youtube.com/watch?v=HIa6NElzUtQ Clip from top gear

Main Demonstrate the effect of frictional forces by attempting to drag a large box across a smooth surface with a forcemeter. Is the force making it easier or more difficult for the box to move?

What is friction? If you rub your hands together, they get warm because there is resistance to the rubbing motion. What is the name of this resistive force? It is called friction. What causes this force? Your hands might look smooth, but on a microscopic level they have rough surfaces, as shown in the photograph. Photo credit: © Martin Dohrn / Science Photo Library When you rub your hands together you feel the resistive force of friction.

Friction and motion Friction always tries to slow moving objects down – it opposes motion. Frictional forces occur when two touching surfaces move past each other, in this case the box moving across the ground. pull of rope on box friction Friction also occurs when things move through air. This is called air resistance. Friction is a contact force and only acts when a force is applied to an object.

What are the sources of friction? Label all sources of friction acting on this bike. pedal bearing air resistance links in chain brake pad Photo credit: © 2008 Jupiterimages Corporation tyre and road wheel bearing

Friction is a force that opposes movement. There is friction when an object moves over a solid surface. There is also friction when something moves through a liquid or gas. The rougher the surface the more friction there is

Surface Amount of force (newtons) Carpet Wood Sand paper Material Metal

11.3 Friction 9

USES PROBLEMS Stopping things moving when they shouldn't. Stopping things moving when the should. Producing heat Wears surfaces down, like shoes, tyres, carpets. Allows you to walk Producing heat. Allows things to move along the ground.

Worksheet Q1a-e

11.3 Friction all around us Why is it harder to stop a car on a wet road?

Streamlining

Lubricants Lubricants are used to reduce friction.

Plenary Students discuss their experimental results and present them in an appropriate format (graph)