Pressure D. Crowley, 2008

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

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

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

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

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

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

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)!

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)

Pressure Bingo

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