Core Case Study: Controlled Scientific Experiment (1)
Hubbard Brook Experimental Forest
Question: What is the environmental impact of forest clear-cutting?
Controlled experiment – isolate variables • Control site• Experimental site
Core Case Study : Controlled Scientific Experiment (2)
Measure loss of water and nutrients
Compare results• 30–40% increase in runoff• 6–8 times more nutrient loss
Draw conclusions• Cause-and-effect relationships
Fig. 2-3, p. 29
Undisturbed(control)watershed
Disturbed(experimental)watershed
Year
Nit
rate
(N
O3
– )
co
nc
entr
ati
on
(mill
igra
ms
pe
r lit
er)
2-1 What Is Science?
Concept 2-1 Scientists collect data and develop theories, models, and laws about how nature works.
Science
Search for order in nature• Observe behavior• Attempt to quantify cause and effect• Make predictions
The Scientific Process (1)
Identify problem/question
Design experiments
Collect data
Formulate hypothesis
Fig. 2-2, p. 25
Scientific lawWell-acceptedpattern in data
Identify a problem
Find out what is knownabout the problem(literature search)
Ask a question to beinvestigated
Perform an experimentto answer the question
and collect data
Analyze data(check for patterns)
Fig. 2-2, p. 25
Make testablepredictions
Propose an hypothesis
to explain data
Use hypothesis to make testable
predictions
Perform an experiment
to test predictions
Accepthypothesis
Scientific theoryWell-tested andwidely accepted
hypothesis
Revisehypothesis
Testpredictions
Scientific theoryWell-tested andwidely accepted
hypothesis Fig. 2-2, p. 25
Stepped Art
Testpredictions
Make testablepredictions
Accepthypothesis
Revisehypothesis
Perform an experimentto test predictions
Use hypothesis to make testable predictions
Propose an hypothesisto explain data
Analyze data(check for patterns)
Scientific lawWell-acceptedpattern in data
Perform an experimentto answer the question
and collect data
Ask a question to beinvestigated
Find out what is knownabout the problem(literature search)
Identify a problem
Results of Science
Goals• Scientific theories• Scientific laws
Degree of certainty and general acceptance• Frontier science• Reliable science• Unreliable science
Scientific Limitations
Limitations – 100% certain?• Absolute proof versus probability• Observational bias• Complex interactions, many variables• Estimates and extrapolating numbers
Science does not answer moral or ethical questions
Science Focus: Easter Island
Solving a mystery• Population crash – cause and effect
Evolving hypotheses• Unsustainable resource use?• Rats?• Disease?• Slave trade?
Science as a process
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.
Building Blocks of Matter (1)
Atomic Theory – elements made from atoms
Atoms• Protons – positive charge• Neutrons – uncharged• Electrons – negative charge
Building Blocks of Matter (2)
Atomic number• Number of protons
Mass number• Neutrons + protons
Isotopes• Same atomic number, different mass
Building Blocks of Matter (3)
Ions• One or more net positive or negative electrical
charges
Chemical formula• Number and type of each atom or ion
Compounds• Organic• Inorganic
Organic Compounds
Carbon-based compounds
Examples• Hydrocarbons• Chlorinated hydrocarbons• Simple carbohydrates• Complex carbohydrates• Proteins• Nucleic acids (DNA and RNA)
Fig. 2-4, p. 30Aluminum ore
Low QualityHigh Quality
Solid
Salt
Coal
Gasoline
Aluminum can
Gas
Solution of salt in water
Coal-fired powerplant emissions
Automobile emissions
2-3 How Can Matter Change?
Concept 2-3 When matter undergoes a physical or chemical change, no atoms are created or destroyed (the law of conservation of matter).
p. 31
Reactant(s) Product(s)
Carbon + Oxygen
C + O2
Black solid Colorless gasColorless gas
Energy
Energy
Energy
Carbon dioxide +
CO2 +
+
Nuclear Changes (1)
Radioactive decay – unstable isotopes• Alpha particles• Beta particles• Gamma rays
Nuclear Changes (2)
Nuclear fission • Large mass isotopes split apart• Chain reaction
Nuclear fusion• Two light isotopes forced together• High temperature to start reaction• Stars
Fig. 2-5a, p. 32
Radioactive decay
Radioactive isotope
Gamma rays
Beta particle (electron)
Alpha particle(helium-4 nucleus)
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. 2-5b, p. 32
Nuclear fission Uranium-235
Uranium-235
Neutron
Fissionfragment
Fissionfragment
Energy
Energy
Energy
Energy
Nuclear fission occurs when the nuclei of certain isotopes with large mass numbers (such as uranium-235) are split apart into lighter nuclei when struck by a neutron and release energy plus two or three more neutrons. Each neutron can trigger an additional fission reaction and lead to a chain reaction, which releases an enormous amount of energy.
Neutron
Uranium-235
Fissionfragment
Fissionfragment
Energyn
n
n
Energy
Energy
n
n
n
Energy
Uranium-235
Uranium-235
Uranium-235
Uranium-235
Uranium-235
Uranium-235
Uranium-235
Uranium-235
Uranium-235 Fig. 2-5b, p. 32
Stepped Art
Fig. 2-5c, p. 32
Nuclear fusion
Fuel
Proton Neutron
Hydrogen-2(deuterium nucleus)
Hydrogen-3(tritium nucleus)
100million °C
Reactionconditions Products
Helium-4 nucleus
Energy
Neutron
Nuclear fusion occurs when two isotopes of light elements, suchas hydrogen, are forced together at extremely high temperaturesuntil they fuse to form a heavier nucleus and release a tremendous amount of energy.
Law of Conservation of Matter
Matter only changes from one form to another
There is no “throwing away”
Environmental implications• Recycle• Reuse• Must deal with wastes and pollutants
2-4 What Is Energy and How Can It Change Its Form?
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, we end up with lower quality or less usable energy than we started with (second law of thermodynamics).
Types of Energy
Potential energy – stored energy• Gasoline• Water behind a dam
Kinetic energy – energy in motion• Wind, flowing water, electricity• Heat – flow from warm to cold• Electromagnetic radiation • wavelength and relative energy
Energy Quality
High-quality energy – concentrated• High temperature heat• Nuclear fission• Concentrated sunlight• High-velocity wind• Fossil fuels
Low-quality energy – dispersed• Heat in atmosphere and ocean
Laws of Conservation of Energy (Thermodynamics)
First law of thermodynamics • Energy input = Energy output
Second law of thermodynamics • Energy use results in lower-quality energy• Dispersed heat loss
Consequences of the Second Law of Thermodynamics (1)
Automobiles• ~6% moves car• ~94% dissipates as low-quality heat into the
environment
Incandescent light bulb• ~5% useful light• ~95% heat
Consequences of the Second Law of Thermodynamics (2)
Living systems• Energy lost with every conversion
Fig. 2-7, p. 34
Solarenergy
Chemical energy(photo-
synthesis)
Mechanicalenergy
(moving,thinking, living)
Chemicalenergy(food)
Wasteheat
Wasteheat
Wasteheat
Wasteheat
2-5 How Can We Use Matter and Energy More Sustainably?
Concept 2-5A The processes of life must conform to the law of conservation of matter and the two laws of thermodynamics.
Concept 2-5B We can live more sustainably by using and wasting less matter and energy, recycling and reusing most matter resources, and controlling human population growth.
High-throughput (High-waste) Economy
Increase flow of matter and energy to boost economy
Environmental capacity?
Fig. 2-8, p. 36
Low-qualityenergy (heat)
High-qualitymatter
High-qualityenergy
Inputs(from environment)
Systemthroughputs
High-wasteeconomy
Outputs(into environment)
Waste andpollution
Low-throughput (Low-waste) Economy
Matter recycling and reuse economy
Mimic nature
Maximize matter cycling with minimal energy input
Fig. 2-9, p. 36
High-quality energy
Waste andpollution
prevention
Low-qualityenergy (heat)
Outputs(into environment)
Systemthroughputs
Waste andpollution
Pollutioncontrol
Low-wasteeconomy
Inputs(from environment)
Energyconservation
High-quality matter
Recycle andreuse
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