1. CHAPTER 2 Science, Matter, Energy, and Systems

2. Core Case Study: A Story About a Forest
Hubbard Brook Experimental Forest in New Hampshire
Compared the loss of water and nutrients from an uncut forest (control site) with one that had been stripped (experimental site)
Stripped site:
30-40% more runoff
More dissolved nutrients
More soil erosion

3. The Effects of Deforestation on the Loss of Water and Soil Nutrients
Figure 2.1: This controlled field experiment measured the effects of deforestation on the loss of water and soil nutrients from a forest. V–notched dams were built at the bottoms of two forested valleys so that all water and nutrients flowing from each valley could be collected and measured for volume and mineral content. These measurements were recorded for the forested valley (left), which acted as the control site, and for the other valley, which acted as the experimental site (right). Then all the trees in the experimental valley were cut and, for 3 years, the flows of water and soil nutrients from both valleys were measured and compared.
Fig. 2-1, p. 31

4. Stepped Art
Fig. 2-1, p. 31

5. 2-1 What Do Scientists Do?
Concept 2-1 Scientists collect data and develop theories, models, and laws about how nature works.

6. Science Is a Search for Order in Nature (1)
Identify a problem
Find out what is known about the problem
Ask a question to be investigated
Gather data through experiments
Propose a scientific hypothesis

7. Science Is a Search for Order in Nature (2)
Make testable predictions
Keep testing and making observations
Accept or reject the hypothesis
Scientific theory: well-tested and widely accepted hypothesis

8. The Scientific Process
Figure 2.2: This diagram illustrates what scientists do. Scientists use this overall process for testing ideas about how the natural world works. However, they do not necessarily follow the order of steps shown here. For example, sometimes a scientist might start by coming up with a hypothesis to answer the initial question and then run experiments to test the hypothesis.
Fig. 2-2, p. 33

9. Ask a question to be investigated
Identify a problem
Find out what is known about the problem (literature search)
Ask a question to be investigated
Perform an experiment to answer the question
and collect data
Scientific law Well-accepted pattern in data
Analyze data (check for patterns)
Propose a hypothesis to explain data
Use hypothesis to make testable projections
Figure 2.2: This diagram illustrates what scientists do. Scientists use this overall process for testing ideas about how the natural world works. However, they do not necessarily follow the order of steps shown here. For example, sometimes a scientist might start by coming up with a hypothesis to answer the initial question and then run experiments to test the hypothesis.
Perform an experiment to test projections
Accept hypothesis
Revise hypothesis
Make testable projections
Test projections
Scientific theory Well-tested and widely accepted hypothesis
Fig. 2-2, p. 33

10. Use hypothesis to make testable predictions
Identify a problem
Find out what is known
about the problem
(literature search)
Ask a question to be
investigated
Perform an experiment
to answer the question
and collect data
Analyze data
(check for patterns)
Scientific law
Well-accepted
pattern in data
Propose an hypothesis
to explain data
Use hypothesis to make testable predictions
Perform an experiment
to test predictions
Test
predictions
Make testable
Accept
hypothesis
Revise
Scientific theory
Well-tested and
widely accepted
hypothesis
Stepped Art
Fig. 2-2, p. 33

11. Testing a Hypothesis
Figure 2.3: We can use the scientific process to understand and deal with an everyday problem.
Fig. 2-3, p. 33

12. Nothing happens when I try to turn on my flashlight.
Observation:
Nothing happens when I try to turn on my flashlight.
Question: Why didn’t the light come on?
Hypothesis: Maybe the batteries are dead.
Test hypothesis with an experiment: Put in new batteries and try to turn on the flashlight.
Result: Flashlight still does not work.
New hypothesis: Maybe the bulb is burned out.
Figure 2.3: We can use the scientific process to understand and deal with an everyday problem.
Experiment: Put in a new bulb.
Result: Flashlight works.
Conclusion: New hypothesis is verified.
Fig. 2-3, p. 33

13. Characteristics of Science…and Scientists
Curiosity
Skepticism
Reproducibility
Peer review
Openness to new ideas
Critical thinking
Creativity

14. Science Focus: Easter Island: Revisions to a Popular Environmental Story
Some revisions to a popular environmental story
Polynesians arrived about 800 years ago
Population may have reached 3000
Used trees in an unsustainable manner, but rats may have multiplied and eaten the seeds of the trees

15. Stone Statues on Easter Island
Figure 2.A: These and many other massive stone figures once lined the coasts of Easter Island and are the remains of the technology created on the island by an ancient civilization of Polynesians. Some of these statues are taller than an average five-story building and can weigh as much as 89 metric tons (98 tons).
Fig. 2-A, p. 35

16. Scientific Theories and Laws Are the Most Important Results of Science
Scientific theory
Widely tested
Supported by extensive evidence
Accepted by most scientists in a particular area
Scientific law, law of nature

17. The Results of Science Can Be Tentative, Reliable, or Unreliable
Tentative science, frontier science
Reliable science
Unreliable science

18. Science Has Some Limitations
Particular hypotheses, theories, or laws have a high probability of being true while not being absolute
Bias can be minimized by scientists
Environmental phenomena involve interacting variables and complex interactions
Statistical methods may be used to estimate very large or very small numbers
Scientific process is limited to the natural world

19. Science Focus: Statistics and Probability
Collect, organize, and interpret numerical data
Probability
The chance that something will happen or be valid
Need large enough sample size

20. 2-2 What Is Matter?
Concept 2-2 Matter consists of elements and compounds, which are in turn made up of atoms, ions, or molecules.

21. Matter Consists of Elements and Compounds
Has mass and takes up space
Elements
Unique properties
Cannot be broken down chemically into other substances
Compounds
Two or more different elements bonded together in fixed proportions

22. Gold and Mercury Are Chemical Elements
Figure 2.4: Gold (left) and mercury (right) are chemical elements; each has a unique set of properties and it cannot be broken down into simpler substances.
Fig. 2-4a, p. 38

23. Chemical Elements Used in The Book
Table 2-1, p. 38

24. Atoms, Ions, and Molecules Are the Building Blocks of Matter (1)
Atomic theory
All elements are made of atoms
Subatomic particles
Protons with positive charge and neutrons with no charge in nucleus
Negatively charged electrons orbit the nucleus
Atomic number
Number of protons in nucleus
Mass number
Number of protons plus neutrons in nucleus

25. Model of a Carbon-12 Atom
Figure 2.5: This is a greatly simplified model of a carbon-12 atom. It consists of a nucleus containing six protons, each with a positive electrical charge, and six neutrons with no electrical charge. Six negatively charged electrons are found outside its nucleus. We cannot determine the exact locations of the electrons. Instead, we can estimate the probability that they will be found at various locations outside the nucleus—sometimes called an electron probability cloud. This is somewhat like saying that there are six airplanes flying around inside a cloud. We do not know their exact location, but the cloud represents an area in which we can probably find them.
Fig. 2-5, p. 39

26. 6 protons 6 neutrons 6 electrons
Figure 2.5: This is a greatly simplified model of a carbon-12 atom. It consists of a nucleus containing six protons, each with a positive electrical charge, and six neutrons with no electrical charge. Six negatively charged electrons are found outside its nucleus. We cannot determine the exact locations of the electrons. Instead, we can estimate the probability that they will be found at various locations outside the nucleus—sometimes called an electron probability cloud. This is somewhat like saying that there are six airplanes flying around inside a cloud. We do not know their exact location, but the cloud represents an area in which we can probably find them.
6 electrons
Fig. 2-5, p. 39

27. Atoms, Ions, and Molecules Are the Building Blocks of Matter (2)
Isotopes
Same element, different number of protons
Ions
Gain or lose electrons
Form ionic compounds pH
Measure of acidity
H+ and OH-

28. Chemical Ions Used in This Book
TABLE 2-2
Table 2-2, p. 40

29. pH Scale
Figure 5 The pH scale, representing the concentration of hydrogen ions (H+) in one liter of solution is shown on the right-hand side. On the left side, are the approximate pH values for solutions of some common substances. A solution with a pH less than 7 is acidic, one with a pH of 7 is neutral, and one with a pH greater than 7 is basic. A change of 1 on the pH scale means a tenfold increase or decrease in H+ concentration. (Modified from Cecie Starr, Biology: Today and Tomorrow. Pacific Grove, CA: Brooks/Cole, © 2005)
Supplement 5, Figure 4

30. Loss of NO3− from a Deforested Watershed
Figure 2.6: This graph shows the loss of nitrate ions (NO3–) from a deforested watershed in the Hubbard Brook Experimental Forest (Figure 2-1, right). The average concentration of nitrate ions in runoff from the experimental deforested watershed was about 60 times greater than in a nearby unlogged watershed used as a control (Figure 2-1, left). (Data from F. H. Bormann and Gene Likens)
Fig. 2-6, p. 40

31. Nitrate (NO3–) concentration (milligrams per liter)60
Nitrate (NO3–) concentration
(milligrams per liter) 40
Disturbed (experimental) watershed
Undisturbed (control) watershed 20
Figure 2.6: This graph shows the loss of nitrate ions (NO3–) from a deforested watershed in the Hubbard Brook Experimental Forest (Figure 2-1, right). The average concentration of nitrate ions in runoff from the experimental deforested watershed was about 60 times greater than in a nearby unlogged watershed used as a control (Figure 2-1, left). (Data from F. H. Bormann and Gene Likens)
Year
Fig. 2-6, p. 40

32. Atoms, Ions, and Molecules Are the Building Blocks of Matter (3)
Two or more atoms of the same or different elements held together by chemical bonds
Compounds
Chemical formula

33. Compounds Used in This Book
Table 2-3, p. 40

34. Organic Compounds Are the Chemicals of Life
Hydrocarbons and chlorinated hydrocarbons
Simple carbohydrates
Macromolecules: complex organic molecules
Complex carbohydrates
Proteins
Nucleic acids
Lipids
Inorganic compounds

35. Glucose Structure
Figure 7 Straight-chain and ring structural formulas of glucose, a simple sugar that can be used to build long chains of complex carbohydrates such as starch and cellulose.
Supplement 4, Fig. 4

36. Amino Acids and Proteins
Figure 8 This model illustrates both the general structural formula of amino acids and a specific structural
formula of one of the 20 different amino acid molecules that can be linked together in chains to form
proteins that fold up into more complex shapes.
Supplement 4, Fig. 8

37. Nucleotide Structure in DNA and RNA
Figure 9 This diagram shows the generalized structures of the nucleotide molecules linked in various numbers and sequences to form large nucleic acid molecules such as various types of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). In DNA, the five-carbon sugar in each nucleotide is deoxyribose; in RNA it is ribose. The four basic nucleotides used to make various forms of DNA molecules differ in the types of nucleotide bases they contain—guanine (G), cytosine (C), adenine (A), and thymine (T). (Uracil, labeled U, occurs instead of thymine in RNA.)
Supplement 4, Fig. 9

38. DNA Double Helix Structure and Bonding
Figure 10 Portion of the double helix of a DNA
molecule. The double helix is composed of two
spiral (helical) strands of nucleotides. Each nucleotide
contains a unit of phosphate (P), deoxyribose
(S), and one of four nucleotide bases: guanine (G),
cytosine (C), adenine (A), and thymine (T). The
two strands are held together by hydrogen bonds
formed between various pairs of the nucleotide
bases. Guanine (G) bonds with cytosine (C), and
adenine (A) with thymine (T).
Supplement 4, Fig. 10

39. Fatty Acid Structure and Trigyceride
Figure 11 The structural formula of fatty acid that is one form of lipid
(left) is shown here. Fatty acids are converted into more complex fat molecules
(center) that are stored in adipose cells (right).
Supplement 4, Fig. 11

40. Matter Comes to Life through Genes, Chromosomes, and Cells
Cells: fundamental units of life; all organisms are composed of one or more cells
Genes
Sequences of nucleotides within DNA
Instructions for proteins
Create inheritable traits
Chromosomes: composed of many genes

41. Cells, Nuclei, Chromosomes, DNA, and Genes
Figure 2.7: This diagram shows the relationships among cells, nuclei, chromosomes, DNA, and genes.
Fig. 2-7, p. 42

42. Each human cell (except for red blood cells) contains a nucleus.
A human body contains trillions of cells, each with an identical set of genes.
Each human cell (except for red blood cells) contains a nucleus.
Each cell nucleus has an identical set of chromosomes, which are found in pairs.
A specific pair of chromosomes contains one chromosome from each parent.
Figure 2.7: This diagram shows the relationships among cells, nuclei, chromosomes, DNA, and genes.
Each chromosome contains a long DNA molecule in the form
of a coiled double helix.
Genes are segments of
DNA on chromosomes that
contain instructions to make
proteins—the building blocks of life.
Fig. 2-7, p. 42

43. A human body contains trillions of cells, each with an identical set
of genes.
Each human cell (except for red
blood cells) contains a nucleus.
Each cell nucleus has an identical set
of chromosomes, which are found in
pairs.
A specific pair of chromosomes
contains one chromosome from each
parent.
Each chromosome contains a long
DNA molecule in the form of a coiled
double helix.
Genes are segments of DNA on
chromosomes that contain instructions
to make proteins—the building blocks
of life.
Stepped Art
Fig. 2-7, p. 42

44. Some Forms of Matter Are More Useful than Others
High-quality matter
Highly concentrated
Near earth’s surface
High potential as a resource
Low-quality matter
Not highly concentrated
Deep underground or widely dispersed
Low potential as a resource

45. Examples of Differences in Matter Quality
Figure 2.8: These examples illustrate the differences in matter quality. High-quality matter (left column) is fairly easy to extract and is highly concentrated; low-quality matter (right column) is not highly concentrated and is more difficult to extract than high-quality matter.
Fig. 2-8, p. 42

46. Solution of salt in water
High Quality
Low Quality
Solid
Gas
Salt
Solution of salt in water
Coal
Coal-fired power plant emissions
Figure 2.8: These examples illustrate the differences in matter quality. High-quality matter (left column) is fairly easy to extract and is highly concentrated; low-quality matter (right column) is not highly concentrated and is more difficult to extract than high-quality matter.
Gasoline
Automobile emissions
Aluminum can
Aluminum ore
Fig. 2-8, p. 42

47. 2-3 What Happens When Matter Undergoes Change?
Concept 2-3 Whenever matter undergoes a physical or chemical change, no atoms are created or destroyed (the law of conservation of matter).

48. Matter Undergoes Physical, Chemical, and Nuclear Changes
Physical change
No change in chemical composition
Chemical change, chemical reaction
Change in chemical composition
Reactants and products
Nuclear change
Natural radioactive decay
Radioisotopes: unstable
Nuclear fission
Nuclear fusion

49. Types of Nuclear Changes
Figure 2.9: There are three types of nuclear changes: natural radioactive decay (top), nuclear fission (middle), and nuclear fusion (bottom).
Fig. 2-9, p. 43

50. Beta particle (electron)
Radioactive decay
Alpha particle
(helium-4 nucleus)
Radioactive isotope
Gamma rays
Figure 2.9: There are three types of nuclear changes: natural radioactive decay (top), nuclear fission (middle), and nuclear fusion (bottom).
Beta particle (electron)
Radioactive decay occurs when nuclei of unstable isotopes spontaneously emit fast-moving chunks of matter (alpha particles or beta particles), high-energy radiation (gamma rays), or both at a fixed rate. A particular radioactive isotope may emit any one or a combination of the three items shown in the diagram.
Fig. 2-9a, p. 43

51. Nuclear fission Uranium-235 Energy Fission fragment n n Neutron n n
Figure 2.9: There are three types of nuclear changes: natural radioactive decay (top), nuclear fission (middle), and nuclear fusion (bottom).
Radioactive isotope Radioactive decay occurs when nuclei of unstable isotopes
spontaneously emit fast-moving chunks of matter (alpha particles or beta particles), high-energy radiation (gamma rays), or both at a fixed rate. A particular radioactive isotope may emit any one or a combination of the three items shown in the diagram.
Fig. 2-9b, p. 43

52. Stepped Art Energy Uranium-235 Neutron Energy n Energy Uranium-235
Fission
fragment
Energy n
Stepped Art
Fig. 2-9b, p. 43

53. Nuclear fusion occurs when two isotopes of light elements, such
Reaction
conditions
Fuel
Products
Proton
Neutron
Helium-4 nucleus
Hydrogen-2
(deuterium nucleus)
100
million °C
Energy
Figure 2.9: There are three types of nuclear changes: natural radioactive decay (top), nuclear fission (middle), and nuclear fusion (bottom).
Hydrogen-3
(tritium nucleus)
Neutron
Nuclear fusion occurs when two isotopes of light elements, such
as hydrogen, are forced together at extremely high temperatures
until they fuse to form a heavier nucleus and release a tremendous
amount of energy.
Fig. 2-9c, p. 43

54. We Cannot Create or Destroy Matter
Law of conservation of matter
Whenever matter undergoes a physical or chemical change, no atoms are created or destroyed

55. 2-4 What is Energy and What Happens When It Undergoes Change?
Concept 2-4A When energy is converted from one form to another in a physical or chemical change, no energy is created or destroyed (first law of thermodynamics).
Concept 2-4B Whenever energy is changed from one form to another in a physical or chemical change, we end up with lower-quality or less usable energy than we started with (second law of thermodynamics).

56. Energy Comes in Many Forms (1)
Kinetic energy
Flowing water
Wind
Heat
Transferred by radiation, conduction, or convection
Electromagnetic radiation
Potential energy
Stored energy
Can be changed into kinetic energy

57. Wind’s Kinetic Energy Moves This Turbine
Figure 2.10: Kinetic energy, created by the gaseous molecules in a mass of moving air, turns the blades of this wind turbine. The turbine then converts this kinetic energy to electrical energy, which is another form of kinetic energy.
Fig. 2-10, p. 44

58. The Electromagnetic Spectrum
Figure 2.11: The electromagnetic spectrum consists of a range of electromagnetic waves, which differ in wavelength (the distance between successive peaks or troughs) and energy content.
Fig. 2-11, p. 45

59. Shorter wavelengths and higher energy
Visible light
Shorter wavelengths and higher energy
Infrared radiation
Longer wavelengths and lower energy
Gamma rays
UV radiation
X rays
Microwaves
TV, Radio waves
0.001
0.01
0.1 1 10
0.1 10
100
0.1 1 10 1 10
100
Wavelengths (not to scale)
Figure 2.11: The electromagnetic spectrum consists of a range of electromagnetic waves, which differ in wavelength (the distance between successive peaks or troughs) and energy content.
Nanometers
Micrometers
Centimeters
Meters
Fig. 2-11, p. 45

60. Potential Energy
Figure 2.12: The water stored in this reservoir behind a dam in the U.S. state of Tennessee has potential energy, which becomes kinetic energy when the water flows through channels built into the dam where it spins a turbine and produces electricity—another form of kinetic energy.
Fig. 2-12, p. 45

61. Energy Comes in Many Forms (2)
Sun provides 99% of earth’s energy
Warms earth to comfortable temperature
Plant photosynthesis
Winds
Hydropower
Biomass
Fossil fuels: oil, coal, natural gas

62. Nuclear Energy to Electromagnetic Radiation
Figure 2.13: Energy from the sun supports life and human economies. This energy is produced far away from the earth by nuclear fusion (Figure 2-9, bottom). In this process, nuclei of light elements such as hydrogen are forced together at extremely high temperatures until they fuse to form a heavier nucleus. This results in the release of a massive amount of energy that is radiated out through space.
Fig. 2-13, p. 46

63. Fossil fuels
Figure 2.14: Fossil fuels: Oil, coal, and natural gas (left, center, and right, respectively) supply most of the commercial energy that we use to supplement energy from the sun. Burning fossil fuels provides us with many benefits such as heat, electricity, air conditioning, manufacturing, and mobility. But when we burn these fuels, we automatically add carbon dioxide and various other pollutants to the atmosphere.
Fig. 2-14a, p. 46

64. Some Types of Energy Are More Useful Than Others
High-quality energy
High capacity to do work
Concentrated
High-temperature heat
Strong winds
Fossil fuels
Low-quality energy
Low capacity to do work
Dispersed

65. Ocean Heat Is Low-Quality Energy
Figure 2.15: A huge amount of the sun’s energy is stored as heat in the world’s oceans. But the temperature of this widely dispersed energy is so low that we cannot use it to heat matter to a high temperature. Thus, the ocean’s stored heat is low-quality energy. Question: Why is direct solar energy a higher-quality form of energy than the ocean’s heat is?
Fig. 2-15, p. 47

66. Energy Changes Are Governed by Two Scientific Laws
First Law of Thermodynamics
Law of conservation of energy
Energy is neither created nor destroyed in physical and chemical changes
Second Law of Thermodynamics
Energy always goes from a more useful to a less useful form when it changes from one form to another
Light bulbs and combustion engines are very inefficient: produce wasted heat

67. Energy-Wasting Technologies
Figure 2.16: Two widely used technologies waste enormous amounts of energy. In an incandescent lightbulb (right), about 95% of the electrical energy flowing into it becomes heat; just 5% becomes light. By comparison, in a compact fluorescent bulb (left) with the same brightness, about 20% of the energy input becomes light. In the internal combustion engine (right photo) found in most motor vehicles, about 87% of the chemical energy provided in its gasoline fuel flows into the environment as low-quality heat. (Data from U.S. Department of Energy and Amory Lovins; see his Guest Essay at CengageNOW.)
Fig. 2-16a, p. 48

68. 2-5 What Are Systems and How Do They Respond to Change?
Concept 2-5 Systems have inputs, flows, and outputs of matter and energy, and feedback can affect their behavior.

69. Systems Have Inputs, Flows, and Outputs
Set of components that interact in a regular way
Human body, earth, the economy
Inputs from the environment
Flows, throughputs of matter and energy
Outputs to the environment

70. Inputs, Throughput, and Outputs of an Economic System
Figure 2.17: This diagram illustrates a greatly simplified model of a system. Most systems depend on inputs of matter and energy resources, and outputs of wastes, pollutants, and heat to the environment. A system can become unsustainable if the throughputs of matter and energy resources exceed the abilities of the system’s environment to provide the required resource inputs and to absorb or dilute the resulting wastes, pollutants, and heat.
Fig. 2-17, p. 48

71. Inputs (from environment) Outputs (to environment) Throughputs
Energy resources
Work or products
Matter resources
System processes
Waste and pollution
Information
Heat
Figure 2.17: This diagram illustrates a greatly simplified model of a system. Most systems depend on inputs of matter and energy resources, and outputs of wastes, pollutants, and heat to the environment. A system can become unsustainable if the throughputs of matter and energy resources exceed the abilities of the system’s environment to provide the required resource inputs and to absorb or dilute the resulting wastes, pollutants, and heat.
Fig. 2-17, p. 48

72. Systems Respond to Change through Feedback Loops
Positive feedback loop
Causes system to change further in the same direction
Can cause major environmental problems
Negative, or corrective, feedback loop
Causes system to change in opposite direction

73. Positive Feedback Loop
Figure 2.18: This diagram represents a positive feedback loop. Decreasing vegetation in a valley causes increasing erosion and nutrient losses that in turn cause more vegetation to die, resulting in more erosion and nutrient losses. Question: Can you think of another positive feedback loop in nature?
Fig. 2-18, p. 49

74. Decreasing vegetation...
... which causes more vegetation to die.
... leads to erosion and nutrient loss...
Figure 2.18: This diagram represents a positive feedback loop. Decreasing vegetation in a valley causes increasing erosion and nutrient losses that in turn cause more vegetation to die, resulting in more erosion and nutrient losses. Question: Can you think of another positive feedback loop in nature?
Fig. 2-18, p. 49

75. Negative Feedback Loop
Figure 2.19: This diagram illustrates a negative feedback loop. When a house being heated by a furnace gets to a certain temperature, its thermostat is set to turn off the furnace, and the house begins to cool instead of continuing to get warmer. When the house temperature drops below the set point, this information is fed back to turn the furnace on until the desired temperature is reached again.
Fig. 2-19, p. 50

76. Temperature reaches desired setting and furnace goes off
House warms
Temperature reaches desired setting and furnace goes off
Furnace on
Furnace off
Figure 2.19: This diagram illustrates a negative feedback loop. When a house being heated by a furnace gets to a certain temperature, its thermostat is set to turn off the furnace, and the house begins to cool instead of continuing to get warmer. When the house temperature drops below the set point, this information is fed back to turn the furnace on until the desired temperature is reached again.
House cools
Temperature drops below desired setting and furnace goes on
Fig. 2-19, p. 50

77. Time Delays Can Allow a System to Reach a Tipping Point
Time delays vary
Between the input of a feedback stimulus and the response to it
Tipping point, threshold level
Causes a shift in the behavior of a system
Melting of polar ice
Population growth

78. System Effects Can Be Amplified through Synergy
Synergistic interaction, synergy
Two or more processes combine in such a way that combined effect is greater than the two separate effects
Helpful
Studying with a partner
Harmful
E.g., Smoking and inhaling asbestos particles

79. The Usefulness of Models for Studying Systems
Identify major components of systems and interactions within system, and then write equations
Use computer to describe behavior, based on the equations
Compare projected behavior with known behavior
Can use a good model to answer “if-then“ questions

80. Three Big Ideas There is no away.
You cannot get something for nothing.
You cannot break even.