FLUID PRESSURE Or feeling a bit stressed lately???
Are you under a lot of pressure? Do you feel a lot of pressure? PRESSURE! Right now, 1000 N of pressure are pushing on the top of your head!
What is pressure? The result of a force distributed over an area Pressure = force = Newton area meters 2 SI unit of pressure is the pascal (Pa) 1 Pa = 1 newton/m 2
Examples If the area of a box touching the ground is 1.5 square meters, and its weight is 2700 newtons, what pressure does the box exert on the ground? A gymnast standing on one hand (area 0.02 m 2 ) pushes down on the ground with a force of 600 N. How much pressure does the gymnast exert on the ground?
So. …….. The greater the area the force is distributed over, the less the pressure
For example: sharp knife vs dull knife Sharp knife exerts a LARGE FORCE over a small area FORCE/ area = PRESSURE Dull knife exerts a small force over a LARGE AREA Force/AREA = pressure
You do the math Sharp knife: area = 1 mm 2 Dull knife: area = 5 mm 2 Force applied to each knife = 5 N Sharp knife = 5/1 = 5N/m 2 Dull knife = 5/5 = 1N/m 2
How about? Soft Bed vs. hard floor Bed exerts force upward equal to your weight Mattress exerts force upward over your whole body Floor only pushes on pressure points which are touching the floor
Another example: Ice skating (or roller blading) A shoe distributes the force (body weight) over a much larger area than the skate So the skate exerts a much higher pressure on the ice than the shoe does The skate pushes into the ice and Voila! You can skate!
So what are fluids? Substances that flow and have no definite shape Examples: gases and liquids
What are some characteristics of pressure in fluids?
Depth effects pressure As depth increases, water pressure increases (directly proportional)
Altitude effects pressure As altitude increase, air pressure decreases (inversely proportional)
Fluids want to... Move from areas of high pressure to areas of low pressure Everything wants to be equal
Standard atmospheric pressure = 14.7 pounds per square inch What happened to this can?
Everything wants to be equal! Pressure on the outside >>>> pressure on the inside So when the can is heated, the can is crushed! Why?????