1. What is science?
2. How is it done these days?
3. The origins of modern science.
4. Laws of motion, gravity.
5. The nature of energy.
6. Conservation of energy.

• Energy is conserved
• Be able to recognize the forms of energy
• Trophic levels
• Sun’s light energy budget on Earth
• Conservation law
• Open and closed systems
• 1st law of thermodynamics
• Age of the earth and how it is heated
• US fuel budget

• A force causes a mass to accelerate, F = ma
• W = Fd, work is done when a force moves a mass by some distance.
• Energy is the ability to do work.
• P = W/t, power is the amount of work done during a period of time
• Forms of Energy:  Kinetic, Potential

• Big bang – all the energy in the universe came from the Big Bang event, so we know that energy can convert to different forms. In some sort of sense, the universe really is just a complete set of all the different forms of energy.
• Examples
1. Nuclear reactions occur in the sun, producing light
2. Light is absorbed by plants converting it to chemical energy
3. We eat plants and convert the chemical energy into kinetic energy of our muscles
4. We climb diving board steps, converting kinetic to gravitational potential
5. We jump off diving board, converting gravitational to kinetic.
6. We hit the water, converting kinetic to heat.
7. And so on, it never ends…
• Every form of energy can be converted into any other form.
• A major emphasis in today’s science is to discover novel sources of energy and ways to convert from one form to another.
• Eg. Light, wind, waterfalls, waves, name some others….
• NREL in Golden CO, photovoltaics, hydrogen

• This is a discussion of how the earth uses the sun’s light energy
• At the top of earth’s atmosphere we get light energy from the sun = 1400 watts/m².
• Simply computing the area of the earth facing the sun at any given time we find that a total of 1.79 x 10¹⁷ watts reaches the outer atmosphere
• I.e. 1.79 x 10¹⁷ joules of energy each sec. (10¹⁴ joules would power your home for 12,000 years)
• 25% gets reflected back to space
• 25% is absorbed by the gases in the atmosphere (converted to kinetic and chemical PE)
• Earth’s surface reflects 5%.
• Leaving 45% to be absorbed on the surface.
• Most of the light heats the ground and evaporates water
• 4% of this 45% is used in photosynthesis. = 2% of the total.

• Now let’s trace this through living organisms
• Define trophic level as consisting of all organisms that get their energy from the same source.
Level 1: all plants that use light through photosynthesis
Level 2: herbivores, animals that eat only plants (cows, rabbits)
Level 3: carnivores, animals that eat only herbivores (wolves, blood-sucking ticks)
Level 4: carnivores that eat only carnivores (killer whales)
Others: things that eat dead and decaying matter, (termites, fungus)
Mixed: omnivores eating from all trophic levels (people)
• Each level uses at most 10% of the available energy, therefore animals from level 4 use less than 2% x .1 x .1 x .1 = .002% of the total energy taken from the sun by life.
• Cost in food follows this, with beef costing 10 times grain, by weight.
• This was true, even in the time of the dinosaurs, 10 herbivores for each carnivore. This is roughly equal to the ratio found in warm-blooded animals today. This arguement is used by some to suggest that dinosaurs were warm-blooded.

• Energy is conserved
• Definition: Conserved: anything whose value remains constant, eg If the number of atoms is constant, then we say that the number of atoms is conserved. For instance, if you eat an apple, the apple is broken all up but the number of atoms is conserved because this number does not change. However, a nuclear reaction that converts uranium to thorium plus helium does not conserve the number of atoms.
• A statement defining that something is conserved is called a conservation law. This is not the same as conservation of waste!
• Definition: System: an imaginary box that contains only the things that you want to study. Eg: pan of water, forest, the entire planet, nervous system, solar system, and ecosystem. This allows us to focus on the parts that interest us.
• Definition: Open system: the system can exchange energy and matter with its surroundings, eg, water in a lake
• Definition: Closed system: isolated, eg, food in a fish tank, or the universe.
• Definition: Thermodynamics: movement of heat
• First law of thermodynamics:

In an closed system, the total amount of energy is conserved.

• Eg: bungy jumper, gravitational energy climbing to top of bridge
Jump and convert to kinetic
Cord stretches, converting to elastic,
Bounce up, converting to kinetic, and then to gravitational again.
Meanwhile cord heats up.
If we ignore friction, then the sum of all this energy remains a constant, equal to the amount of gravitational PE at the beginning.

• In the mid 1800’s the question about “how old is the earth?” was addressed by thermodynamics.
• It was assumed that the earth formed from accretion of interstellar dust.
• It must have been hot from the conversion of kinetic energy of the colliding bodies.
• Assuming no other source of heat, then the length of time that it would have taken to cool was about 100 million years.
• This was a big problem for geology because evidence was that the earth was billions of years old.
• The problem was not resolved until the 1890’s when radioactivity was discovered. Mass gets converted to heat. Thus, with the calculations of thermodynamics we estimate that earth gets more than half of its heat from the decay of radioactive materials inside.

• Dead organic materials collect in layers at the bottom of seas etc. and eventually become buried.
• Heat and pressure convert the matter into deposits of fossil fuels, the most common of which are coal, natural gas and petroleum.
• It takes about 10 million years to do this conversion. Thus these resources are classified as nonrenewable resources.
• 90% of our nation’s energy comes from this.
1 billion tons of coal,
2 ½ billion barrels of oil each year.
The cleanest oil and best coal will be gone during our lifetime. A couple hundred years more for the rest. We need alternative sources.
• What does the rest of world use? (dung and wood).
• A new source of hydrocarbon has been found in the last 10 years, called methane hydrates. This is ice that is found in or on ocean floors deeper than 300 meters, and in the tundra as permafrost. It is estimated that there is more than twice as much gas in this form than in all other hydrocarbon deposits known. We do not know how to mine it.