3. Pressure
Force and pressure P.8 of 13

 What happens if we change the force? On this page, you will do an imaginary experiment to find out how pressure varies with force. To keep it a fair test, the area will be the same all the way through. Look at the acrobat in the foreground of picture 3.3.
 Picture 3.3 How do the pressures compare? All the acrobats weigh the same.

He weighs 600 N and the total area of his feet is 300 cm2.

What is the pressure under his feet?
[Fill in the equation, then work out the answer].

 Pressure = = N/cm2 Don't type in any commas - just numbers

 Summary                                           Close pressure is the force per unit area pressure is proportional to the force we measure pressure in pascals (Pa) pressure = force ÷ area 1 Pa = 1 N/m2
Now the acrobat is carrying his twin brother. So the total weight is 1200 N. What is the new pressure on the ground?
 Pressure = = N/cm2

Finally, the third brother (of triplets) joins them. (They all the weigh the same).

What is the pressure now?

 Pressure = = N/cm2
Well done. You've got them all right.

Let's look at a table of the results:

 Force N Pressure N/cm2 600 2 1200 4 1800 6

The pressure is proprotional to the force:

• when the force doubles, the pressure doubles
• when the force triples, the pressure triples