2PressureSince fluids take different shapes, the concept of a force on a fluid is better described as PRESSURE. You can’t really “push” a fluid but you can exert pressure on it.Pressure is the amount of force applied to a fluid per unit surface areaBike tire has 100 psi (pounds per square inch)Car tire has 35 psi (pounds per square inch)
3Formula to calculate pressure Pressure (Pa) = Force (N)area (m2)ORP = F/aP is pressure measured in Pascals (Pa)F is force exerted measured in Newtons (N)a is surface area measured in m2
4Pressure in a LiquidIn a liquid, pressure depends on the density of the liquid and the depthHigher the density the higher the pressureIncreased depth means increased pressureSCUBA divers experience increased pressure the deeper they dive….you can feel it in your ears!!!
5Pressure in a GasIn a gas, pressure depends on the temperature, volume and number of gas particlesHigher temperature means higher pressure because the molecules are moving fasterIncreasing the volume results in lowering the pressure because there is more room for the molecules to moveIncreasing the number of gas molecules will increase the pressure
11Archimedes’ Principle Since the pressure in a liquid increases with depth, an upward force called “buoyancy” is exerted on objects placed in liquidsArchimedes’ Principle: the magnitude of the buoyant force will equal the weight of the fluid displaced by the object
12Archimedes’ Principle explains why some objects will float in water and some will sink. It also explains why objects feel “lighter” when underwater.Why does a steel ship float in water?It all has to do with the shape of the hull and the weight of water displaced by the ship’s hull.
15Archimedes’ Principle If the buoyant force is less than the force of gravity (Fb<Fg) the object will sinkIf the buoyant force is greater than the force of gravity (Fb>Fg) the object will floatIf the buoyant force is equal to the force of gravity (Fb=Fg) the object will maintain the same depth
18Bernoulli’s Principle or how a 875 000 pound airplane can fly
19Bernoulli’s Principle When a fluid or gas is in motion, like the wind in the air, its pressure varies with its speedBernoulli’s Principle: the higher the speed of the fluid or gas, the lower its pressureThis explains how a plane can fly (Fig. 3.38, p. 98)
20Bernoulli’s Principle When the force from the lift exceeds that of gravity, the plane rises into the air.