Chapter 10

 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.

 Don’t forget about Plasma!  Considered a fluid state  Plasma can conduct electricity, gas cannot  Think of lightening bolts, stars, neon signs, fluorescent bulbs…

 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

 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

 The density ρ of an object is its mass per unit volume:  Density is a property of any pure substance  Units are kg/m 3  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 is a scalar quantity  In the SI system the unit of pressure is the pascal (Pa) which is 1N/m 2  Pressure equals force divided by surface area P = F A

:  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!

 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).

 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

 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 (F b )  The buoyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object FgFg FbFb

 Explains why ships can be made of steel and still float.  Applied in submarines  Fish 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.

 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

 Above a certain speed flow becomes turbulent  Turbulent flow has eddies  Eddies absorb energy

 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.

 Real fluids have internal friction as adjacent layers of fluid move past one another

 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.

 Zitewitz. Physics: Principles and Problems  y-2.gif y-2.gif  Giancoli, Douglas. Physics: Principles with Applications 6th Edition  Walker, James. AP Physics: 4 th Edition. 2010