Forces in Fluids Fluid pressure BouyancyHydraulics Bernoulli’s Principle
Fluid Pressure EEEExerts a “push” on an object AAAActs in all directions
Pressure Force that acts over a certain area. F P A Pressure = Force ÷ Area Force is measured in Newtons, area in cm 2, so pressure is N/ cm 2.
Example problem A woman weighs 750N. She is standing on high heels with a total area of 2cm 2 touching the ground. How much pressure does she exert? F 750N P A P 2cm 2 750N ÷ 2cm 2 = 375N/cm 2
Example problem 2 An elephant weighs 75,000N. She is standing on 4 big feet. Each foot is 50cm in diameter. How much pressure does she exert? Area of feet = 4·π·d = 628cm 2 F 75,000N P A P 628 cm 2 75,000N ÷ 628cm 2 = 119 N/cm 2
How can this be? An elephant weighs 100 times as much as a woman, yet it exerts less pressure on the floor?
What puts a greater force on a bamboo floor? A two ton car? An African elephant? A 125 pound woman with high heels? Measured in pounds per square inch, (PSI), a car has a load of 28 to 30 PSI, an elephant 50 to 100 PSI, and a 125 pound woman with high heels, when she takes a step and those hit the floor, 2,000 PSI!
Bouyancy Force of a fluid that pushes up on an object. Makes the object seem lighter
Archimedes Principle The buoyant force on an object is equal to the weight of the fluid displaced. An object will float in a liquid if the density of the object is less than the density of the liquid.
If the weight of the water displaced is less than the weight of the object, the object will sink Otherwise the object will float, with the weight of the water displaced equal to the weight of the object. Archimedes' Principle explains why steel ships float
Will It Float? Will It Float? The density of the granola bar is greater than the density of the water.