FLUIDSChapter 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.

Liquids and gases both flow, and are called fluids.

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…

ONE MORE VIEW OF THE 4 STATES OF MATTER…

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 solidsAlso classified as viscous liquids

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

DENSITY AND SPECIFIC GRAVITY

The density ρ of 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

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

: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!

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).

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

BUOYANCY & ARCHIMEDES’ PRINCIPLE

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

Fg

Fb

PRACTICAL APPLICATIONSExplains why ships can be made of steel

and still float.Applied in submarinesFish use swim bladders to control depth

The buoyant force can be calculated

The difference between the buoyant force and the object’s weight determines whether an object sinks or floats

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.

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

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

TURBULENT FLOW Above a certain speed

flow becomes turbulent

Turbulent flow has eddies

Eddies absorb energy

BERNOULLI’S PRINCIPLEWhere 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.

VISCOSITY Real fluids have internal friction as

adjacent layers of fluid move past one another

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.

REFERENCES Zitewitz. Physics: Principles and Problems.

2004 http://www.bestsynthetic.com/graphics/visc

osity-2.gif Giancoli, Douglas. Physics: Principles with

Applications 6th Edition. 2009. Walker, James. AP Physics: 4th Edition. 2010