1. Systems & Energy Review Notes
Tuesday, August 15th, 2017

2. Energy = the ability to do work or transfer heat
Kinetic Energy = moving energy
Ex: wind, heat, electromagnetic radiation
Potential Energy = stored energy
Unlit match, nuclear energy stored in nuclei of atoms, chemical energy (energy in food)

3. Kinetic vs. Potential Energy

4. Energy Quality
High quality energy – concentrated; high capacity to do useful work
Nuclear fission, burning coal, gasoline
Low quality energy – dispersed; little capacity to do useful work
Heat of the ocean, burning wood

5. Laws of Thermodynamics
1st law: Energy cannot be created or destroyed, it can only change form!
2nd Law: When energy changes form, it loses quality; usually in the form of heat

6. What are systems and how do they respond to change?
Open system: exchanges of matter and energy occur across boundaries
Closed system: No matter and energy exchanges across boundaries (occur way less)
Inputs: additions to a system
Outputs: losses from a system

7. System Analysis
Determine the inputs and outputs of a system and evaluate change
Steady state: when inputs = outputs so the system isn’t changing

8. Positive and Negative Feedback Loops
Positive: causes a system to change further in the same direction
Causes a system to change in the opposite direction; stabilizing
**** Positive is not necessarily “good,” negative is not necessarily “bad”

9. Positive Feedback Loop

10. Negative feedback loop
Negative feedback loop = output from a system moving in one direction acts as input
That moves the system in the other direction
Input and output neutralize one another
Stabilizes the system
Example: predator – prey interactions
Most systems in nature

11. Positive feedback loop
Positive feedback loop = instead of stabilizing a system, it drives it further toward one extreme or another
Exponential growth in human population, erosion, melting sea ice
Rare in nature
But is common in natural systems altered by humans

12. Tipping point – causing a fundamental shift in the behavior of a system
Synergy – when two or more processes interact so that the combined effect is greater than the sum of their separate effects
Chaos occurs in a system when there is no pattern and it never repeats itself

13. Energy Efficiency Refers to the measure of useful energy, a ratio
amount of work done: total amount of energy introduced to the system in the first place
Efficiency of a product can be measured by:
% efficiency = (output / input) x 100
Output is mechanical work/energy (watts or joules)
Input is the quantity of work/energy
Cannot exceed 100% because of the law of conservation of energy

14. Energy: Is the product of force times distance Can be destroyed
Is always conserved
Cannot be transformed
Cannot be conserved

15. Considering inputs to a pool and outputs from it, the pool will be in a steady state when:
inputs exceeds outputs
outputs cease
inputs equal outputs
outputs exceeds inputs
inputs cease

16. As an example of second-law efficiency, a gasoline powered car might have an efficiency of 65%, but an electric car might have an efficiency of 35% from the original fossil fuel (coal burned to make electricity) to the end use. This is because:
burning large volumes of coal in an electric utility is less efficient than utilizing small quantities of gasoline
electricity is a lower quality energy source than gasoline
every step in converting energy to a different form is less than 100% efficient, and the electric car has an extra step
energy always goes from a higher quality form to a lower
electric car technology is not as far advanced as gasoline technology