1. Pressure
D. Crowley, 2008

2. Friday, April 12, 2019
Pressure
To be able to calculate pressure

3. Pressure
Look at the pictures below – who exerts more pressure on the ground, the elephant, or the lady in stilettos?
versus

4. Pressure Pressure is exerted when a force is applied over an area
Pressure is measured in Newtons per square meter (N/m2) also known as Pascals (Pa) – it can also be measured in N/cm2
With a big enough area, you can stay on top of the powder…
1N/m2 = 1Pa

5. Pressure To work out pressure you need to know two things: -
The force (or weight) applied
The area over which the force (or weight) acts upon
Force
(F)
Pressure
(P)
Area
(A)
Pressure = Force  Area Area = Force  Pressure Force = Pressure x Area

6. Pressure Calculate the pressure: -
If the weight of the elephant is 10’000N with an area of 4500cm2
If the weight of the lady is 600N with an area of 150cm2
versus
Pressure = 10’000 ÷ 4500
=2.2N/cm2
Pressure = 600 ÷ 150
=4N/cm2

7. Pressure
Pressure can be extremely useful - drawing pins have a large round end for you to push the sharp end into a notice board
The round end applies a low pressure to your thumb, but the sharp end applies a high pressure to the notice board, so it pushes in

8. 4 Legs
Explain why leaning on one chair leg, instead of the normal four, is not sensible (in terms of pressure)
Remember, the force (your weight) does not change
However, you’ve now reduced the area by 4x, so the pressure applied by the one remaining leg is 4x as much (bad for the chair and the floor)!

9. Experiment
Measure how much pressure your exert on the ground (test two feet; one foot; your hands; your head; your bum etc…)
Using graph paper, draw around your chosen exertion points, and work out your area (count the number of squares inside – each small square is 1cm2)
Find your weight (using the Newton meters)
Finally calculate your pressure (force ÷ area)

10. Pressure Bingo

11. Questions
48/12
44/2
49/7
88/8
80/5
2500/50
1500/10
308/14
832/13
756/18
495/15
81/9
39/3 4 22 7 11 16 50
150 64 42 33 9 13
350/5
315/3
56/2
630/3
1080/10
96/1
144/2
1000/50
18/1
64/8
147/7
8600/100 70
105 28
210
108 96 72 20 18 8 21 86