Visualising what happens at surfaces for grip and slip

What the Activity is for

To help children describe the world by:

• recognising that sliding rough surfaces past each other has a warming effect
• recognising that grip forces vary as the surfaces vary

What to Prepare

• friction hand puppet pairs: slippy and grippy (grippy can be made of reversed leather, slippy of parachute nylon – see what materials are to hand)
• a varied collection of flat surfaces: carpet tiles, hardboard, linoleum
• a pair of nail brushes

What Happens During this Activity

Model two surfaces slipping past each other using a pair of scrubbing brushes, with the long bristles lightly engaged, so that they are able to ping past each other as you move the brushes along. Draw attention to the pinging bristles. Ask how to prevent the surfaces sliding (push the brushes together more). Now you'll have grip and not slip. Draw attention to the lack of pinging in the bristles. Make links between the pinging and lack of pinging and expecting to feel something different. Allow the children to pull a friction puppet over a surface that's rough enough so that they feel warmth. Elicit this feeling by questioning, and link to the pinging.

Relate this to lifting the tin, feeling warmth when slip forces are at work, but not when grip forces are at work.

Teacher Tip: Slip forces are dissipative and warm things up. Grip forces are not, and don't warm things up.

You might go further by leading a discussion on phenomena where there is warming, and where not. This could be linked back to the hunt for slip and grip forces.