When you catch a deep-sea fish, why does its eyes pop-out? FLUID MECHANICS How is electricity generated at the bottom of dams? When you catch a deep-sea fish, why does its eyes pop-out? Why do your ears pop on an airplane or while climbing up mountains?

Pressure Pressure is equal to the force applied to a surface, divided by the area.                                                                             

Equations for Pressure Pressure = Force/surface area Pressure = Newtons (Kg x m/s/s) side x side Units are in Pascals or N/m²

Fluid A substance that can easily change its shape, such as liquids and gases. The molecules in a fluid have a certain amount of force (mass and acceleration) and exert pressure on surfaces they touch.

FLUID PRESSURE All the molecules add up together to make up the force exerted by the fluid.

Gravity creates an air pressure of 10.13N/m³ at sea level. Air has a mass of 1Kg/m³ AIR PRESSURE Gravity creates an air pressure of 10.13N/m³ at sea level.

1 atmosphere = 760 mmHg = 29.92 inHg = 14.7 lb/in2 = 101.3 KPa

Pressure and Elevation Air Pressure decreases as elevation increases.

The whole system is a low pressure, but it dramatically decreases towards the eye of the hurricane. Very Low pressure Pressure always flows from high to low, which creates the high velocity winds. Higher Pressure

Barometric Pressure The barometer is used to forecast weather. Decreasing barometer means stormy weather and an increasing barometer means warmer weather.

Measuring Pressure A manometer is a U-shaped tube that is partially filled with liquid. Both ends of the tube are open to the atmosphere. A container of gas is connected to one end of the U-tube. If there is a pressure difference between the gas and the atmosphere, a force will be exerted on the fluid in the U-tube. This changes the equilibrium position of the fluid in the tube. Could incorporate personal response system questions from the College Physics by G/R/R 2E ARIS site (www.mhhe.com/grr), Instructor Resources: CPS by eInstruction, Chapter 9, Questions 2, 3, 13 and 17. Casao

From the figure: At point C Also The pressure at point B is the pressure of the gas. Pgauge easily remembered as “hot dog”

A Barometer The atmosphere pushes on the container of mercury which forces mercury up the closed, inverted tube. The distance d is called the barometric pressure. From the figure: and Atmospheric pressure is equivalent to a column of mercury 76.0 cm tall.

Water pressure increases with depth. Pressure and Depth P = ρgh where P = Pressure ρ = density of fluid g = gravity h = height of fluid Water pressure increases with depth. When the liquid is pressing against a surface there is a net force directed perpendicular to the surface. If there is a hole in the surface, the liquid initially moves perpendicular to the surface. At greater depths, the net force is greater and the horizontal velocity of the escaping liquid is greater.

At any point within a liquid, the forces that produce pressure are exerted equally in all directions. Pressure increases vertically downward. Pressure constant horizontally.

Columnar Fluid Pressure (sometimes called gauge pressure) pressure due to a column of fluid of height h and mass density D; The pressure of a liquid at rest depends on the density and depth of the liquid. Liquids are practically incompressible, so except for changes in the temperature, the density of a liquid is normally the same at all depths.

Columnar Fluid Pressure At a given depth, a given liquid exerts the same pressure against any surface - the bottom or sides of its container, or even the surface of an object submerged in the liquid to that depth. Pressure a liquid exerts depends only on its density and depth. Total pressure (or absolute pressure) Pabsolute on a submerged surface equals the pressure the liquid exerts plus the atmospheric pressure Po (1 atm = 1.013 x 105 Pa) .

Fluid Pressure Pressure of a liquid does not depend on the amount of liquid. Neither the volume or total weight of the liquid matters. If you sampled water pressure at 1 m beneath a large lake surface and 1 m beneath a small pool surface, the pressure would be the same. The fact that water pressure depends on depth and not on volume is illustrated by Pascal vases. Water surface in each of the connected vases is at the same level. Occurs because the pressures at equal depths beneath the surface are the same.

Forces Exerted By a Fluid When the liquid is pressing against a surface there is a net force directed perpendicular to the surface. If there is a hole in the surface, the liquid initially moves perpendicular to the surface. At greater depths, the net force is greater and the horizontal velocity of the escaping liquid is greater.

Pascal’s Principle When force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.

Transmission of Pressure: Pascal’s Principle. Pascal’s Principle: A CHANGE IN PRESSURE IN A CONFINED FLUID IS TRANSMITTED WITHOUT CHANGE TO ALL POINTS IN THE FLUID. Ex. Hydraulic lift. Hydraulic piston apparatus uses an incompressible fluid to transmit pressure from a small cylinder to a large cylinder. According to Pascal’s Principle, the pressure in the small cylinder resulting from the application of F1 to a frictionless piston is transmitted undiminished to the larger piston.

Transmission of pressure: Pascal’s Principle. P1 = P2 A2 is larger than A1, so the force exerted by the large piston is greater than the force exerted on the small piston. AMA (actual mechanical advantage) for hydraulic lift:

Hydraulic Devices By changing the size of the pistons, the force can be multiplied.

3. What is the total force of the right Piston? F=P A= 2000 N/m2 x 20m2 = 40,000N 20 m2 .002m2 1. What is the pressure of the left piston? 2. What is the pressure of the right Piston? P= F/A = 4 N/.002 m2= 2000 Pa 2000Pa

Hydraulic Brakes The hydraulic brake system of a car multiplies the force exerted on the brake pedal.