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Fluids

Fluids . Chapter 10. 10.1 Phases of matter . The three common phases of matter are solid, liquid, and gas. A solid has a definite shape and size. A liquid has a fixed volume but can be any shape. A gas can be any shape and also can be easily compressed.

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Fluids

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  1. Fluids Chapter 10

  2. 10.1 Phases of matter • The three common phases of matter are solid, liquid, and gas. • A solid has a definite shape and size. • A liquid has a fixed volume but can be any shape. • A gas can be any shape and also can be easily compressed. • Liquids and gases both flow, and are called fluids.

  3. How many states of matter again? • Don’t forget about Plasma! • Considered a fluid state • Plasma can conduct electricity, gas cannot • Think of lightening bolts, stars, neon signs, fluorescent bulbs…

  4. One more view of the 4 states of matter…

  5. Solids and liquids • Solids and liquids not always easily distinguished • Some solids are made of orderly particles frozen in a fixed pattern, called a crystal lattice . (ex. Crystalline quartz) • Other solids don’t have a regular crystal structure but do have definite volume and shape (ex. Butter) These are amorphous solids • Also classified as viscous liquids

  6. Thermal expansion of solids • Engineers design gaps called expansion joints into concrete and steel to allow for expansion • When solids are heated KE of the particles increases, they vibrate and move farther apart, weakening attractive forces between particles, ultimately causing expansion • Different materials expand at different rates

  7. Density and Specific gravity • The density ρof an object is its mass per unit volume: • Density is a property of any pure substance • Units are kg/m3 • The specific gravity (SG) of a substance is the ratio of its density to that of water • It is a ratio and has no units • Ex. SG of lead is 11.3 and of alcohol is 0.79

  8. Pressure • Pressure is a scalar quantity • In the SI system the unit of pressure is the pascal (Pa) which is 1N/m2 • Pressure equals force divided by surface area P = F A

  9. Pressure in Fluids : • The pressure at a depth h below the surface of the liquid is due to the weight of the liquid above it. • For incompressible fluids we can calculate the pressure using the following formula • Gases are very compressible and their density can change with depth!

  10. Atmospheric Pressure and Gauge Pressure • Earth’s atmosphere is a fluid, and therefore the pressure changes with depth • At sea level the atmospheric pressure is about this is called one atmosphere (atm).

  11. Pascal’s Principle • If an external pressure is applied to a confined fluid the pressure at every point within the fluid increases by that amount • Imagine squeezing a tube of toothpaste from the bottom. The pressure exerted at the bottom is transmitted and forces the fluid out at the top. • Many applications: hydraulic lifts, car brakes

  12. Buoyancy & Archimedes’ principle Fg • Objects that float on water are buoyant • Gravity acts downward on the object • The increase in pressure with increasing depth creates an upward force called the buoyant force (Fb) • The buoyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object Fb

  13. practical applications • Explains why ships can be made of steel and still float. • Applied in submarines • Fish use swim bladders to control depth

  14. The buoyant force can be calculated • The difference between the buoyant force and the object’s weight determines whether an object sinks or floats

  15. If the object’s density is less than that of water, there will be an upward net force on it, and it will rise until it is partially out of the water.

  16. This principle also works in the air; this is why hot-air and helium balloons rise.

  17. Fluids in Motion; fluid dynamics • Streamlining is the flow of fluids around objects, or ensuring efficiency of movement through air • Auto and aircraft engineers spend time and $ to streamline their designs so they’ll require less energy to move • If the flow of a fluid is smooth, it is called streamline or laminar flow

  18. Turbulent Flow • Above a certain speed flow becomes turbulent • Turbulent flow has eddies • Eddies absorb energy

  19. Bernoulli’s principle • Where the velocity of a fluid is high, the pressure is low, and where the velocity is low, the pressure is high • Lift on an airplane wing is due to the different air speeds and pressures on the two surfaces of the wing.

  20. Viscosity • Real fluids have internal friction as adjacent layers of fluid move past one another

  21. Surface Tension and Capillarity • The surface of a liquid at rest is not perfectly flat; it curves either up or down at the walls of the container. This is the result of surface tension, which makes the surface behave somewhat elastically.

  22. References • Zitewitz. Physics: Principles and Problems. 2004 • http://www.bestsynthetic.com/graphics/viscosity-2.gif • Giancoli, Douglas. Physics: Principles with Applications 6th Edition. 2009. • Walker, James. AP Physics: 4th Edition. 2010

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