Friction KS 3 Forces Friction always tries to

Friction KS 3 Forces

Friction always tries to slow moving objects down. It makes things hard to move and gives things ‘grip’. Sometimes this can be useful, sometimes it is not. E. g. You cannot walk unless there is friction between your shoes and the ground – this is useful. TASK Write numbers 1 -6 in your margin. As you look through the next slides, write down the letter which best matches. You only have 10 seconds to decide!

1… so that the tyre does not skid on the road. a b c d e f

2…because it would slow the wheel down. a b c d e f

3… so your hands can grip the handle-bars. a b c d e f

4. . . so your bottom does not slip off the seat a b c d e f

5… because it would be hard to steer the bike. a b c d e f

6… so that your feet do not slip off the pedals. a b c d e f

How did you do? a-5 b-3 c-4 d-2 e-6 f-1

Non Contact forces Friction is a CONTACT force, the surfaces have to touch for the force to have an effect. Some forces exist where contact is not necessary. Gravitational pull – an apple falling on your head Magnetism – a magnet attracting paper clips Electrostatic forces – running water being attracted to a charged plastic rod.

Friction Object being pulled across surface Interlocking here causes friction TASK Copy these notes. Friction always tries to slow moving objects down. It is created whenever two touching objects or surfaces move past each other. Friction also occurs when things move through air. This is called air resistance or drag.

Reducing the effect of friction TASK Think back to the bike, how do you reduce the friction in places where it is not wanted? Oil or grease acts as a lubricant, it fills the ‘ridges and valleys’ of the surface (when looked at under a microscope). This means the surfaces can move smoothly over one another, without interlocking.

What key facts have you learned? §…. §…. Transfer activity: Write two list titles in your book useful and not useful. Look at the picture of the bike on the next slide, list the parts under the correct headings, places where you WANT friction, useful; where you do NOT, not useful.