Braking uses slip forces

What the Activity is for

To help children describe the world by:

• emphasising that slip forces result in warming
• recognising that mechanical braking relies on slip forces

What to Prepare

• friction hand puppet pairs: slippy and grippy
• a spinning disk to slow down

Teacher Tip: To check if the disk is appropriate, try spinning it up, then slowing it down with the slippy puppet: it should take more than 20 rotations. For the grippy puppet, it should be less than 2 rotations.

What Happens During this Activity

It may be that a discussion about bike brakes is the best way in, but this will depend on whether the children have and use bicycles. in other cases you may be better off with an image of formula one car brakes glowing. The link to the warming that's felt when slowing down a spinning disk with the hand gloves should be made. You'll need to experiment with the speed and surface in order to ensure that hands do not get burnt, but that the disk can be brought to a halt in a reasonable time (a few seconds).

Teacher Tip: You might stimulate a discussion about the results of braking using grip forces, or how braking is achieved using drag forces.