# How air and water move things

Post on 26-Feb-2016

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How air and water move things. Bernoullis law and Magnus force. Hydrostatic pressure. Blaise Pascal. P = gh. Hydrostatic pressure. = fluid/gas density g =acceleration due to gravity h =height. P = gh. Pressure in liquid/gas is isotropic. It acts equally in all directions - PowerPoint PPT PresentationTRANSCRIPT

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How air and water move thingsBernoullis law and Magnus forceHydrostatic pressure Blaise Pascal

P = gh

Hydrostatic pressure

P = gh

Pressure in liquid/gas is isotropic. It acts equally in all directions Pressure is force per unit area Due to the gravity, pressure at a given level equals to the weight of the column of liquid/gas above this level over a unit area=fluid/gas densityg=acceleration due to gravityh=heightPressure measurement: liquid (mercury) manometer

Hydrostatic pressure of air and water

Atmospheric pressure

Hydrostatic pressure

P = gh

Bernoullis principle

For a non-turbulent flow of fluid or gas As speed increases, the pressure in the fluid or gas decreases.Bernoullis equationP + v2+ gh = const

P=pressure of the fluid/gas along the streamlinev=velocity of the fluid/gas along the streamlineg=acceleration due to gravityh=height=fluid/gas densityThe Bernoullis equation expresses conservation of enegy. It assumes that:The fluid/gas has a constant densityThe fluid/gas is traveling in a steady flowThere is no frictionThe fluid/gas is non viscous and incompressableBernoullis principle

Bernoullis equation

Derivation of Bernoulli

Accelerationa-aAcceleration in the non-inertial frame moving with the flowBecause velocity of the fluid/gas flow has changed (increased) from v1 to v2 , there must be a force which causes it to accelerate while passing the distance l. For simplicity, let us assume constant acceleration a.Distance lDerivation of Bernoulli

Accelerationa-aAcceleration in the non-inertial frame moving with the flowThe equivalence principle: In an accelerated reference frame moving with the flow we can calculate the pressure difference as if it were a pressuredifference in a gravitational field, P = P2 - P1 = a lDistance lInertial force and the equivalence principle

Inertial force and the equivalence principle

Inertial force and the equivalence principle

The inertial mass relates force and acceleration in the Newtons first law of motion: F = ma. The gravitational mass determines force of gravitational attraction in the Newtons law of gravity: (= mg).The inertial mass and the gravitational mass are equal.

Derivation of Bernoulli

Accelerationa-aAcceleration in the non-inertial frame moving with the flowKinematics of motion with constant acceleration, a, gives,v2 = v1 + at, l = v1t + at2 = (v22 - v12 ) /(2a)where t is the time it took the flow to pass the distance l. Distance l

Derivation of Bernoulli

Accelerationa-aAcceleration in the non-inertial frame moving with the flowCombining the two results gives the Bernoulli equation,

P = P2 - P1 = a l = (v22 - v12 )/2Distance lTorricellis law

v2/2+Patm= gh+Patm =>v2 = 2ghPatmPatmExamples of Bernoulli principle

Sprayers and atomizers

Ventouri effect and applicationsDental Saliva Ejector Hose With Water Venturi Suction System

Ventouri wine aerator

Ventouri detergent intake system in a powerwasherDraft by wind in a chimney

Becomes important for wind velocity v > 2gh( 10 m/s for h 5 m).

Pitot tube

Pitot tube

Pitot tubes

Spectacular effect Bernoulli

Ships passing on parallel course

Ships sailing side by side can get too close together (as in picture above, at a certain point during the refueling). When this happens, the Venturi effect takes over, and the ships will head toward an unavoidable collisionBernoulli pull by passing trains

An airfoil in a wind tunnel

Airfoil lift schematics

An airfoil creates a region of high pressure air below the wing, and a low pressure region above it. The air leaving the wing has a downward flow creating the Newtonian force. Bernoulli pressure field creates the downwash. Flying machines

The Magnus effectWhere the cylinder is turning into the airflow, the air is moving faster and the pressure is lower Where the cylinder is turning away from the airflow, the air is moving slower and the pressure is greaterThe cylinder moves towards the low pressure zone

Curveballs

The Magnus effect! stitches help the ball to catch the air the baseball curves towards the lower air pressurePhysics of golf: dimples on the ball and the Magnus effect

Typical ball spin-rates are:3,600 rpm when hit with a 10 driver (8 launch angle) at a velocity of 134 mph7,200 rpm when hit with a 5 iron (23 launch angle) at a velocity of 105 mph10,800 rpm when hit with a 9 iron (45 launch angle) at a velocity of 90 mphTopping the ball (i.e. when the bottom of the club-face hits the ball above its center) will cause the ball to spin in the other direction - i.e. downward - which will cause the ball to dive into the ground.Dimples cause the air-flow above the ball to travel faster and thus the pressure on the ball from the top to be lower than the air pressure below the ball. This pressure difference (i.e. more relative pressure from below than on top) causes the ball to lift (Magnus effect) and stay in the air for a longer time.Flettner rotor ship Buckau (Baden-Baden)

1927Flettner rotor ship E-1 (Kiel 2010)

Flettner rotor sail catamaran

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