Pressure

Pressure

• 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

F
P
A
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