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Forces in Fluids

1) Fluids are substances that can flow and take the shape of their container. Pressure is defined as force per unit area and increases with depth in fluids. 2) Pascal's principle states that pressure increases are transmitted equally throughout a fluid in a closed container. Hydraulic systems use this principle to magnify force. 3) Pressure increases linearly with depth in fluids due to the weight of the fluid above pressing down. Atmospheric and water pressure are greatest at sea level and the deepest point underwater, respectively.

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Forces in Fluids
Review Newton’s Laws Explanation Summary First The velocity of an object will not change unless it is acted on by an unbalanced force. inertia Second When an object is acted on by an unbalanced force, it will accelerate in the direction of that force. F=ma Third For every action there is an equal and opposite reaction. action-reaction
Fluids A fluid is any substance that lacks a definite shape and has the ability to flow. Fluids = liquids and gasses Viscosity describes how “sticky” or strongly attracted fluid molecules are to each other
Pressure: the amount of force acting on a unit of area. P = F/A Measured in units of pascals (N/m 2 ). One pascal (Pa) = 1 N of force per square meter Pressure
Calculating Pressure Pressure = force or P = F area A Weight = 100 N A foot = 5 m 2 A snowshoe = 50 m 2 P foot = 100 N = 20 Pa 5 m 2 P snowshoe = 100 N = 2 Pa 50 m 2
Pascal’s Principle When a force is applied to a fluid in a closed container, an increase in pressure is transmitted equally to all parts of the fluid. That pressure (force per area) is undiminished throughout the fluid. The force is usually a push or squeeze.
Force Pumps Fluids are moved from one place to another by increasing the pressure with a push or squeeze Ex.: bicycle pumps, tubes of toothpaste, your heart How it works
Hydraulic Devices
P = Force/Area (Area = length x width) 10N ÷ 1cm 2 First change cm 2 to m 2 1 cm = .01 m .01 m x .01 m = .0001 m 2 10 N ÷ .0001 m 2 = 100,000 N/ m 2 (Pascals) 1cm 1cm
Pressure = force or P = F and F= PA area A F 1 = 10 N A 1 = 1 m 2 P = 10 N 1 m 2 Pressure = 10 Pa If A 2 = 50 m 2 then what is the force on the bigger piston? F = P x A, so F 2 = 10 Pa x 50 m 2 F 2 = 500 N
Video Explanation
Pressure & Depth The weight of a fluid can exert a pressure on anything underneath it. Pressure increases with depth due to the weight of the fluid above pressing down. Atmospheric pressure differs with elevation. 100 kPa at sea level (1008 milibars or 15 lbs/in 2 ) The higher up in the atmosphere, the less air there is pushing down, so the lower the pressure will be.
Pressure & Depth Water pressure also increases with depth. The water pressure at the bottom of a lake is greater than at the surface because of all the water (and atmospheric gas) pressing down.
At which point is water pressure the greatest? They are all equal. Only depth affects pressure.