Pressure

Tack pressing into wood vs finger Knife cutting box Side of knife vs edge Tack pressing into wood vs finger We can use the same force in two ways Less concentrated – less pressure More concentrated – more pressure

http://www.kscience.co.uk/animations/pressure.htm

Pressure Force per unit area How concentrated the force is P – Pressure (Pa or N/m2) F – Force (N) A – Area (m2)

Units for Pressure Pa – Pascal – a piece of newspaper lying on a desk kPa – kilopascal - ** Psi – pounds per square inch - ** Atm – Atmosphere – pressure of air at sea level

Ex 1: A car typically weighs about 2000kg. If a car has four wheels and each wheel makes contact with the ground over an area of approximately 20cm by 15cm, what pressure should the wheel be filled to?

Car Tire – 300 kPa or 44 psi

Atmospheric Pressure Created by the weight of air pushing down on us 100 kPa or 1 atm

Example 2 David sits on a toboggan. The dimensions of the sled touching the ground are 0.50m by 2.0m. If David’s mass is 70 kg, what is the pressure of the sled on the snow? Ans: 6.9x102Pa

Pressure Technology Snow shoes

Iron Lung

Pg 228 # 1,3-5,7,8