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

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)

Kinetic vs. Potential Energy

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

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

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

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

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”

Positive Feedback Loop

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

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

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

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

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

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

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