Making the connection to force and area

What the Activity is for

Here you can show that there is a connection between the force generated, the area over which molecules bombard a surface and the pressure.

What to Prepare

• the interactive object (see below)
• a video of a large soft tyre on a slow moving object

What Happens During this Activity

Show the video first. Draw attention to the support that the tyres give to the tractor. Ask what is in the tyres. Ask what happens to the tyre if more mass is put on the tractor. What about if the tyres are deflated a little? What will happen to the track left by the tractor in each case? These questions – you can add some more if you feel the need – all point towards the particles in the tyres supporting the mass of the tractor by bombarding the walls of the tyre. More mass, or lower pressure in the tyre, lead to a larger area of tyre in contact with the ground.

Now move to the second interactive and put the bike tyres in order of increasing pressure, given that it's the same rider in each case.