(Dr. Evil doesn't "do" phases, but in physics we do, in two different contexts--phases of matter, and the phase relations between waves.)
Phases of matter. Show diagram at top of page 109. Gas, liquid, solid. And what the process of
converting from one to another is called.
What determines whether a given substance is in the solid, liquid or gas
phase? The temp and pressure!
Solid has a definite volume and shape. Liquid has definite volume but no definite shape. A gas has no definite volume or definite shape.
Most solids have a microscopic crystalline structure (lattice), and some have a MACROscopic, visible crystalline structure—quartz crystal, diamonds, other gems. Two substances mentioned in book that have “amorphous” structure are glass and asphalt. Don’t have a particular melting temp, where bonds are broken and solid becomes liquid. Remember melting and latent heat of fusion.
Kinetic theory of gases. How do you smell perfume, by some kind of smell rays being emitted by the liquid? No, by individual molecules of the perfume being deposited in your nasal passages/olfactory glands. How do the molecules get there? By being converted from liquid to gas and bouncing in all directions off air molecules. Some of these bounce into your nose.
Kinetic Theory describes a gas as consisting of molecules (or atoms) moving independently in all directions at high speeds. Confined gas molecules bounces off walls of container, and molecules bounce off each other. See pages 116 and 117.
Four variables needed: pressure, volume, temp and number of molecules in the container. How does the pressure of the gas vary as V, T, and N are varying? Well, using the symbol α as shorthand for “is proportional to,” we have: P α N, P α T, and P α 1/V.
Combining these gives P α NT/V, the ideal gas law, which can be written as an equation if Bolzmann’s constant k is used: P = kNT/V. Kicking V over to the left side gives the familiar
“Ideal gas” means a model of a gas in which no forces act between the molecules or atoms constituting the gas, they merely collide with each other like billiard balls and collide with the walls of the container and go on their merry way. (But, of course, like billiard balls, where the bounce of a collision is ultimately due to electromagnetic forces, there must be some very short range electromagnetic or other force acting in a collision, or the molecules/atoms would not even sense each other’s presence.)
The first law of thermodynamics is THE CONSERVATION OF ENERGY. In all processes, including thermodynamic ones, energy is neither created nor destroyed. When heat is added to a closed system it is converted into either the internal energy of the system or into doing work. Can be written as simple equation:
Engines do useful work. They make something move, whether it’s a generator rotating in a power plant to produce electricity, your car moving down the road, or electrons moving in a wire. Many, but not all, engines operate by using a source of heat, such as a boiler in an electric power plant or the heat of combustion that moves the pistons in your car. Electricity supplied by batteries or by electric motors are exceptions—they don’t use heat to do work, they use electrons directly, by forcing the electrons to move and consequently to do work. In doing work they produce unwanted heat, though, so thermodynamics also applies to them.
Idealized examples of a heat engine and a heat pump are shown in the book. A heat engine uses heat to do work, and heat pump, such as AC unit, refrigerator, or real heat pump, takes work and uses it to move heat from colder environment to hotter environment.
First law doesn’t rule out heat flowing SPONTANEOUSLY from colder to hotter object. Common sense does, though! And in fact, there is also a law that tells what can and can’t happen thermodynamically—the 2nd Law of Thermodynamics. Heat can’t spontaneously flow from hotter to colder object.
The 2nd law can also be expressed as: the disorder of an isolated system never decreases. Entropy is a mathematical measure of how much disorder a system has, so the other way of stating the 2nd law is: the entropy of an isolated system never decreases.
Entropy has been decreasing on earth, but this is due to energy input from the sun. For the solar system itself, a good approximation to an isolated system, entropy is increasing.
Third law: it’s impossible to attain a temperature of absolute zero. Reason: it would take an infinite amount of work. This is like trying to reach the speed of light: it takes more and more work to increase the kinetic energy of an object as it approaches the speed of light. As absolute zero is approached, it takes more work to remove heat and lower the temp.
(There's also a "zeroth law" of thermodynamics.)
Now, on to ...
Wavelength: the length of one complete wave (thus is measured in meters or other length units).
Period: reciprocal of frequency. So f = 1/T. The time it takes a wave to travel a distance of one wavelength.
EX: Let f= 4HZ. Then 4 wavelengths pass by a point in one second.
Amplitude: the maximum displacement of the wave.
This can be good in the case of making music or singing, because the “resonant cavity” of the instrument or the singer’s throat and nasal cavity will amplify the sound. It can be bad for a structure like a bridge, a wine glass, a building or moving part on a car.
Oh, yeh, we can't forget phases. This is the relationship in time or distance of where the peaks and valleys of two or more waves are located relative to each other. We can have IN phase waves (peaks and valleys of one are lined up with peaks and valleys of another), OUT OF phase waves (peaks of one wave are lined up with valleys of another), and all possibilites in between.
Phases of matter. Show diagram at top of page 109. Gas, liquid, solid. And what the process of
converting from one to another is called.
What determines whether a given substance is in the solid, liquid or gas
phase? The temp and pressure!
Solid has a definite volume and shape. Liquid has definite volume but no definite shape. A gas has no definite volume or definite shape.
Most solids have a microscopic crystalline structure (lattice), and some have a MACROscopic, visible crystalline structure—quartz crystal, diamonds, other gems. Two substances mentioned in book that have “amorphous” structure are glass and asphalt. Don’t have a particular melting temp, where bonds are broken and solid becomes liquid. Remember melting and latent heat of fusion.
Kinetic theory of gases. How do you smell perfume, by some kind of smell rays being emitted by the liquid? No, by individual molecules of the perfume being deposited in your nasal passages/olfactory glands. How do the molecules get there? By being converted from liquid to gas and bouncing in all directions off air molecules. Some of these bounce into your nose.
Kinetic Theory describes a gas as consisting of molecules (or atoms) moving independently in all directions at high speeds. Confined gas molecules bounces off walls of container, and molecules bounce off each other. See pages 116 and 117.
Four variables needed: pressure, volume, temp and number of molecules in the container. How does the pressure of the gas vary as V, T, and N are varying? Well, using the symbol α as shorthand for “is proportional to,” we have: P α N, P α T, and P α 1/V.
Combining these gives P α NT/V, the ideal gas law, which can be written as an equation if Bolzmann’s constant k is used: P = kNT/V. Kicking V over to the left side gives the familiar
PV
= kNT
“Ideal gas” means a model of a gas in which no forces act between the molecules or atoms constituting the gas, they merely collide with each other like billiard balls and collide with the walls of the container and go on their merry way. (But, of course, like billiard balls, where the bounce of a collision is ultimately due to electromagnetic forces, there must be some very short range electromagnetic or other force acting in a collision, or the molecules/atoms would not even sense each other’s presence.)
Thermodynamics: 1st law and heat engines; 2nd
law (Entropy); 3rd law.
Thermodynamics
is about the dynamics of heat. It deals
with heat production, heat flow, and the conversion of heat to work. In dynamics or mechanics, we have Newton’s 3
laws. In thermoshermo, we have also
three laws. Nobody alone discovered them
all, though. Several people contributed
to each one, actually, over the course of 50 to 60 years in the 19th
century.
The first law of thermodynamics is THE CONSERVATION OF ENERGY. In all processes, including thermodynamic ones, energy is neither created nor destroyed. When heat is added to a closed system it is converted into either the internal energy of the system or into doing work. Can be written as simple equation:
H =
ΔEi + W.
Engines do useful work. They make something move, whether it’s a generator rotating in a power plant to produce electricity, your car moving down the road, or electrons moving in a wire. Many, but not all, engines operate by using a source of heat, such as a boiler in an electric power plant or the heat of combustion that moves the pistons in your car. Electricity supplied by batteries or by electric motors are exceptions—they don’t use heat to do work, they use electrons directly, by forcing the electrons to move and consequently to do work. In doing work they produce unwanted heat, though, so thermodynamics also applies to them.
Idealized examples of a heat engine and a heat pump are shown in the book. A heat engine uses heat to do work, and heat pump, such as AC unit, refrigerator, or real heat pump, takes work and uses it to move heat from colder environment to hotter environment.
First law doesn’t rule out heat flowing SPONTANEOUSLY from colder to hotter object. Common sense does, though! And in fact, there is also a law that tells what can and can’t happen thermodynamically—the 2nd Law of Thermodynamics. Heat can’t spontaneously flow from hotter to colder object.
The 2nd law can also be expressed as: the disorder of an isolated system never decreases. Entropy is a mathematical measure of how much disorder a system has, so the other way of stating the 2nd law is: the entropy of an isolated system never decreases.
Entropy has been decreasing on earth, but this is due to energy input from the sun. For the solar system itself, a good approximation to an isolated system, entropy is increasing.
Third law: it’s impossible to attain a temperature of absolute zero. Reason: it would take an infinite amount of work. This is like trying to reach the speed of light: it takes more and more work to increase the kinetic energy of an object as it approaches the speed of light. As absolute zero is approached, it takes more work to remove heat and lower the temp.
(There's also a "zeroth law" of thermodynamics.)
W A V E S
And their properties.
Waves carry energy: a shaking or vibrating of matter—a
disturbance, the book says—causes energy to be released in the form of
waves. The energy can be carried in
air—or in any gas or liquid—in the form of sound waves. If the vibrating object is electrically
charged, it emits electromagnetic waves, which can travel in a vacuum (empty
space).
Waves are of two basic types, longitudinal and
transverse. Longitudinal waves
oscillate parallel to their direction of travel. EX:
Sound waves. See fig 6.3. Transverse waves oscillate perpendicular
to their direction of travel. EX: waves
on a string and electromagnetic waves.
Fig. 6.4.
Wave characteristics:
wavelength, frequency, period, amplitude, velocity.
Wavelength: the length of one complete wave (thus is measured in meters or other length units).
Frequency: Number
of oscillations that occur during a given time, usually taken to be one
second. Unit is hertz, of Hz: 1 Hz is
one oscillation, or one cycle, per second.
Period: reciprocal of frequency. So f = 1/T. The time it takes a wave to travel a distance of one wavelength.
EX: Let f= 4HZ. Then 4 wavelengths pass by a point in one second.
Amplitude: the maximum displacement of the wave.
Speed of light: 3x
10^8 m/s or 186,000 miles per second.
Speed of sound in air at room temp, 20 degrees C, is 344
m/s or 770mph.
Doppler effect: increasing frequency as object emitting
the waves approaches you, decreasing frequency as object moves away from
you.
Resonance: when an object is made to vibrate at one of
its characteristic or natural frequencies. Standing waves are created, as shown
in 6.18.
This can be good in the case of making music or singing, because the “resonant cavity” of the instrument or the singer’s throat and nasal cavity will amplify the sound. It can be bad for a structure like a bridge, a wine glass, a building or moving part on a car.
Oh, yeh, we can't forget phases. This is the relationship in time or distance of where the peaks and valleys of two or more waves are located relative to each other. We can have IN phase waves (peaks and valleys of one are lined up with peaks and valleys of another), OUT OF phase waves (peaks of one wave are lined up with valleys of another), and all possibilites in between.
