Joy of Science Discovering the matters and the laws of the universe

Transcription

1 November 12, 2012 Joy of Science Discovering the matters and the laws of the universe Key Words Universe, Energy, Quantum mechanics, Chemical reaction, Structure of matter (Earth, Evolution of life, Ecosystem, Environment will be taught in next semester) Unless otherwise noted, all pictures are taken from wikipedia.org

2 Course schedule n n n n n n n n n n n n n n n Week1 (10/1) - Science as a way of knowing Week2 (10/15) - The ordered Universe Week3 (10/22) - Unification of the laws of the earth and the universe Week4 (10/29) - Energy Week5 (11/12) - Heat and the second law of thermodynamics Week6 (11/19) - Electricity and Magnetism Week7 (11/26) - Waves and electromagnetic radiation Week8 (12/3) - The atom Week9 (12/10) - Quantum mechanics Week10 (12/17) - Atoms in Combination: the chemical bonds Week11 (12/24 (Mon) à 12/25 (Tue)) - Chemical reactions Week12 (1/7) - Modern materials Week13 (1/21) - Nuclear power Week14 (1/28) - The ultimate structure of matter Week15 (2/4) Group Discussion day, final report due date * Winter vacation starts on 12/27, Thursday

3 Review

4 Review The great chain of energy n Work: In scientific speaking, work is done when a force is exerted over distance work (joules) = force (newtons) X distance (meters): W = F x d n Energy: the ability to do work. If a system is capable of exerting a force over a distance, then that system possesses energy. (è same units used for work) n Power: the amount of work done divided by the time it takes to do that work power (watts) = work (joules) / time(seconds): P = W / t Electrical power unit: watts Work = Energy (joules) = power (watts) X time (seconds)

5 Review The great chain of energy n Work: In scientific speaking, work is done when a force is exerted over distance work (joules) = force (newtons) X distance (meters): W = F x d n Energy: the ability to do work. If a system is capable of exerting a force over a distance, then that system possesses energy. (è same units used for work) n Power: the amount of work done divided by the time it takes to do that work power (watts) = work (joules) / time(seconds): P = W / t Electrical power unit: watts Work = Energy (joules) = power (watts) X time (seconds) Energy unit in your electric bill? A: kwh (kilowatt-hour)! Energy (kwh) = power (kilowatt) X time (hour)

6 Review Forms of energy n Kinetic energy: energy associated with moving objects kinetic energy (joules) = ½ X mass (kg) X [speed (m/s)] 2 : EK = ½ X m X v 2 n Potential energy: energy waiting to be released gravitational potential energy, chemical potential energy, electrical potential energy, and elastic potential energy - In any case, energy is stored, ready to do work! gravitational potential energy (joules) = mass (kg) X g (m/s 2 ) X height (m) : EP = m X g X h n Heat, thermal energy, is the random kinetic energy of atoms and molecules Particles making up all matter move around and vibrate! - All matter is made of minute objects called atoms - Discrete collections of two or more atoms are called molecules n Mass is a form of energy Einstein s equation: energy (joules) = mass (kg) X [speed of light (m/s) ] 2 E = mc 2

7 Interchangeability of energy n The flow and the form conversion of energy from the Sun to human body chemical energy of cells light Sun plants and tissues human chemical energy into kinetic energy muscles motion (kinetic E) à climb a flight of stairs (gravitational potential E) à stretch a rubber band (elastic potential E) à rub hands together (Heat) n Energy in one form can be converted into others

8 The first law of thermodynamics

9 The first law of thermodynamics: Thermodynamics: the study of the movement of heat this term used for the science of heat, energy, and work System: A system can be thought of an imaginary box into which you put some matter and energy that you would like to study - open system: if the system under study can exchange matter and energy with its surroundings, the system is open. Ex) a pan full of water being heated on a stove - closed or isolated system: if matter an energy in a system do not freely exchange with their surroundings, the system is closed. Ex) the system of Earth and it s primary energy source, the Sun Conservation law: if a physical attribute is constant and unchanging therefore it is conserved, there is an associated conservation law

10 The first law of thermodynamics: The first law of thermodynamics n The first law of thermodynamics: In an isolated system the total amount of energy, including heat, is conserved è The law of energy conservation è The kind of energy in a given system can change, but the total amount cannot!

11 The first law of thermodynamics: Energy is conserved n Energy is something like an economy with an absolutely fixed amount of money! You can earn it, store it in a bank or under your pillow, and spend it here and there. But the total amount of money doesn t change because it passes through your hands. n For example, when a bungee jumper launches herself into space, some of the gravitational potential changes into kinetic energy, some into elastic potential energy, and some into the increased temperature of the surroundings. è But the total amount of energy, in a closed system, should be the same amount as the energy when you started with. (gravitational) potential

12 Heat and the second law of thermodynamics Why is it easier to tear something down than to build it Temperature, heat transfer, convection, conduction, radiation, absolute zero, second law of thermodynamics, efficiency, entropy

13 Contents n Introduction n Three modes of heat transfer n The second law of thermodynamics

14 1. Introduction

15 Nature s direction n Throughout the universe, there are some natural tendency for things to become less orderly with time! n The tendency of all systems to evolve from improbable to more probable states accounts for the directionality that we see in the universe around us!!! Ex) Perfume scent disperses through a room when the perfume bottle is open Billiard balls tend to be scattered than get together

16 Terms with heat n Atoms never sit still, but move always while distributing their kinetic energy so called, thermal energy or internal energy. n In order to understand the nature of heat and its movement, let us define three terms first: Heat, Temperature, and Specific heat capacity.

17 Heat n Heat: A form of energy that moves from a warmer object to a cooler object à Heat is, therefore, energy in motion. n Calories: A common unit of energy defined by the amount of heat required to raise 1 gram of room- temperature water by 1 degree Celsius in temperature (In science, room temperature is usually taken to be either 20 or 25 degrees Celsius)

18 Temperature n Temperature: A term that compares how vigorously atoms in a substance are moving and colliding in different substance à The larger the temperature difference between two objects, the more rapidly heat is transferred.

19 Temperature n Temperature: A term that compares how vigorously atoms in a substance are moving and colliding in different substance à The larger the temperature difference between two objects, the more rapidly heat is transferred. n Temperature scales: Every scale requires two easily reproduced temperatures for calibration freezing and boiling points of pure water * Celsius scale : 0 and 100 degrees for freezing and boiling (degrees Celsius: most common) * Kelvin scale : same degrees as Celsius, with 100 increments (Kelvins: scientific) between the freezing and boiling points of water 0 o C = K 100 o C = K * 0 K: absolute zero the temperature at which it is impossible to extract any heat

20 Temperature conversions n It is often necessary to convert from one temperature scale to another Fahrenheit scale (degrees Fahrenheit): 32 and 212 degrees for freezing and boiling, respectively degrees F = ( 9/5 X degrees C ) + 32 degrees C = (degrees F 32) X 5/9

21 Specific heat capacity n Specific heat capacity: A measure of the ability of a material to absorb heat The quantity of heat required to raise the temperature of 1 gram of that material by 1 degree Celsius

22 Specific heat capacity n Specific heat capacity: A measure of the ability of a material to absorb heat The quantity of heat required to raise the temperature of 1 gram of that material by 1 degree Celsius n When we boil water in a copper pot, - it doesn t take long to raise the temperature of a copper pot to above the boiling point of water, because copper- like most metals- heats up rapidly as it absorbs heat; - it takes much more time to boil water in the pot è Water absorbs 10 times more heat per gram than copper to raise its temperature à The ability of water to store thermal energy is bigger than that of copper. In fact, Water has the largest heat capacity of any common substance.

23 2. Three modes of heat transfer

24 Three modes of heat transfer Heat transfer n You can not prevent heat from moving from an object at high temperature to its cooler surroundings! n Heat transfer: The process by which heat moves from one place to another n There are three basic mechanisms of heat transfer: Conduction, Convection, and Radiation

25 Three modes of heat transfer Conduction n If a piece of metal is heated at one end, the atoms and their electrons at that end begin to move faster à They vibrate and collide with other atoms father away from the heat source à A chain of collision occurs farther and farther è è Energy is transferred to molecules farther away from the heat source

26 Three modes of heat transfer Conduction (cont d) n Conduction: An energy transfer mode between bodies of matter due to temperature difference through the action of individual atoms or molecules that are linked together by chemical bonds n Thermal conductivity: The ability to transfer heat from one molecule to the next by conduction. Materials differ in their thermal conductivity. * Heat conductor: It moves heat rapidly. Ex) metals copper, silver, aluminum. * Heat insulator: It resists the flow of heat transfer. Ex) glass, paper, wood

27 Three modes of heat transfer Convection n Convection: The transfer of heat by the bulk of fluid, such as air or water. n Convection cell: Each of regions of rising and sinking fluid. Ex) Boiling water in a pot on a stove has a rolling, churning motion as the water moves and mixes through convection, and the places where water bubbles up and where bubbles tend to collect are convection cells. n Heat is carried from the burner through the convection of the water and is eventually transferred to the atmosphere. è Convection is thus a very efficient way of transferring heat

28 Three modes of heat transfer Radiation n Radiation: The transfer of heat by electromagnetic radiation, a form of wave energy Ex) Glowing red hot above a fireplace or an electric heater: infrared radiation è You perceive heat b/c of the energy that the infrared radiation carries to your hand

29 Three modes of heat transfer Radiation n Radiation: The transfer of heat by electromagnetic radiation, a form of wave energy Ex) Glowing red hot above a fireplace or an electric heater: infrared radiation è You perceive heat b/c of the energy that the infrared radiation carries to your hand n All objects in the universe radiate energy in this way : Under normal circumstances, as an object gives off radiation to its surroundings, it also receives radiation from those surroundings è No net loss of energy under a kind of equilibrium set up n Radiation is the only kind of energy that can travel through the emptiness of space. n In the real world, all three types of heat transfer occur all the time

30 Energy transfer n Convection n Convection zone n Conduction n Radiation

31 Convection Conduction zone Conduction Radiation

32 3. The second law of thermodynamics

33 The second law of thermodynamics The second law of thermodynamics n There is a direction to energy s flow! n The second law of thermodynamics states the common sense of the direction of energy flow n The second law of thermodynamics in different statements 1. Heat will not flow spontaneously from a cold to a hot body 2. You cannot construct an engine that does nothing but convert heat to useful work 3. Every isolated system becomes more disordered with time è These three statements appear differently, but they are actually logically equivalent!!

34 The second law of thermodynamics 1. Heat will not flow spontaneously from a cold to a hot body n This statements describe the behavior of two objects at different temperatures: From everyday observations, we find that in our universe heat flows in only one direction, from hot to cold n This statement explains at the molecular level: Faster-moving molecules tend to share their energy with slower-moving ones by collisions n This statement tells us that: If you wish to cool something down, this action cannot take place spontaneously è you must supply energy à A refrigerator will not work unless it is plugged in!

35 The second law of thermodynamics 2. You cannot construct an engine that does nothing but convert heat to useful work n Energy can be defined as the ability to do work! n This second statement tells us that Whenever energy is transformed from heat to another type, some of that heat must be dumped into the environment and is unavailable to do work è perpetual motion is impossible! Source Energy Heat Engine Heat loss Environment Work electricity, potential energy,

36 The second law of thermodynamics 2. You cannot construct an engine that does nothing but convert heat to useful work (cont d) n For example, when fossil fuels are burned to produce a hightemperature reservoir and generate electricity, a large portion of energy must simply be thrown away * High temperature reservoir: Exploding hot-gas mixture * Low temperature reservoir: Atmosphere into which the heat of compression is dumped Fossil fuels Heat High temperature Engine Heat loss Environment Low temperature Work electricity, potential energy,

37 The second law of thermodynamics 2. You cannot construct an engine that does nothing but convert heat to useful work (cont d) n Efficiency quantifies the loss of useful energy Efficiency is obtained by comparing the temperature difference between the high temperature and low temperature reservoirs with the temperature of the high temperature reservoir efficiency (percent) = (hot temperature cold temperature)/ hot temperature X 100

38 The second law of thermodynamics 3. Every isolated system becomes more disordered with time n This statement describes the tendency of systems all around us to become increasingly disordered Ex) A carefully cleaned room gets messy. A brand new car becomes dirty and scratched. All our bodies gradually get old and wear out.

39 The second law of thermodynamics 3. Every isolated system becomes more disordered with time (cont d) n The meaning of order : A number of objects any small like atoms or big ones like automobiles - contained a system are positioned in a completely regular and predictable pattern n The meaning of disorder : Objects in a system are randomly situated, without any obvious pattern n Highly ordered configurations are less probable: Almost possible configurations are disordered è Ordered (low or small entropy): low probability Disordered (high or large entropy): high probability * Definition of Entropy: a measure of disorder

40 The second law of thermodynamics The second law of thermodynamics n The entropy of an isolated system remains constant or increases.

41 The second law of thermodynamics The second law of thermodynamics n Entropy: It was named after the Greek word for a transformation Definition of entropy: a measure of disorder n In probability theory, the entropy of any arrangement of atoms is related to the number of possible ways that you can achieve that arrangement n Examples of increase of entropy: - Without careful chemical and physical controls, atoms and molecules tend to become more intermixed - Without careful driving, collections of automobiles tend to become more disordered

42 The second law of thermodynamics The second law of thermodynamics n The entropy of an isolated system remains constant or increases. Refrigerator!???

43 The second law of thermodynamics The second law of thermodynamics n The entropy of an isolated system remains constant or increases. : One part of a system can become more ordered, while another part of the system becomes more disordered. Ex) A freezer with a power code è The system s total entropy must increase!

44 Quiz 1 n Eventually, all energy generated on the Earth is returned to space as 1. heat 2. gravitational energy 3. work 4. potential energy

45 Quiz 1 n Eventually, all energy generated on the Earth is returned to space as 1. heat 2. gravitational energy 3. work 4. potential energy

46 Quiz 2 n Which of the following statements is not consistent with the second law of thermodynamics? 1. All isolated systems will tend to remain ordered indefinitely 2. Heat will not flow spontaneously from a cold body to a hot body 3. No engine is one hundred percent efficient in converting energy to work 4. The evolution of more complicated forms of life on Earth does not annul the second law

47 Quiz 2 n Which of the following statements is not consistent with the second law of thermodynamics? 1. All isolated systems will tend to remain ordered indefinitely 2. Heat will not flow spontaneously from a cold body to a hot body 3. No engine is one hundred percent efficient in converting energy to work 4. The evolution of more complicated forms of life on Earth does not annul the second law

48 Quiz 3 n A fire transfers most of its heat by 1. convection 2. conduction 3. radiation 4. infusion

49 Quiz 3 n A fire transfers most of its heat by 1. convection 2. conduction 3. radiation 4. infusion

50 Quiz 4 n All isolated systems will spontaneously tend toward disorder. The phenomenon is referred to as 1. thermal inefficiency 2. heat transfer 3. entropy 4. thermal conductivity

51 Quiz 4 n All isolated systems will spontaneously tend toward disorder. The phenomenon is referred to as 1. thermal inefficiency 2. heat transfer 3. entropy 4. thermal conductivity

52 Next topic is, Electricity and Magnetism : Chapter 3