Module 5 (FINALLY!)

Energy is the ability to do work (heard that before?)

Units are joules ("jowles in England), and a few others (calories, Calories, BTU, kWh)

Power is how fast you can do the work (climbing stairs or running up stairs), so Power = work/time

Units are Watts (joules per second or j/s) among others

Energy->Joules (work~amount of water)

Power->Watts (how fast the work is done~flow)

demo: walking/running upstairs-----------------

KE/PE: Kinetic and potential energy

PE: chemical bonds, height, spring

KE: motion, freewheel, flowing air/water

temp: KE=1/2mv^2 (macro level)

molecular level:

KE=3/2kT, so T prop to v^2 of molecules

EMR: shorter wavelengths more energy e.g. UV, X-rays

Light is one form of EMR or electromagnetic radiation (needs no medium, so we get light from the sun through the vacuum of space)

What you need to know: EMR has higher energy with higher frequency (e.g. ultraviolet light damages DNA, infrared heat can only burn)

See visible spectrum:

Energy can be potential (ability to do work) like altitude or chemical bonds or kinetic (see Kinesias in Lysistrata), the energy of motion or heat (molecules in motion, KE = 3/2kT)

Temperature is not heat, but the average speed of the molecules...

Temp in the upper atmosphere is 900°C but you'd freeze there, as there is no atmosphere to conduct the heat to you.

Interesting fact: Concorde passengers could not touch the windows, not because they were too cold from the altitude, but too hot from the air friction of the plane going 2x the speed of sound.

1. you can't win (no such thing as more than 100% efficiency)

2. you can't break even (not even 100% is possible, there is always a "heat tax" on every reaction)

3. you can't get out of the game (all reactions tend towards disorder, the "heat death" of the universe, or ∆S>0 for the universe)

Chemical version:

1. energy cannot be created or destroyed
2. energy can move, but always at a cost (entropy, disorder increases, ∆S>0 universe)

Efficiency is the amount you get out of any energy reaction, divided by the amount that went in, always less than 100%

efficiency; never 100%, 30-60% common

Human 35% efficiency, diesel engine 60%, Formula one racing car: 55%

Energy "quality" is the degree of organization of the energy (sugar molecules vs. heat coming from your body, or well organized gasoline "octane" molecules breaking into heat, CO2 and H2O)

Entropy: degree of disorder in any system, all reactions tend towards more disorder (e.g. your closet or bedroom-tell this to your parents)

energy quality-entropy, disorder, e.g. closet ∆S>0, takes energy input to reduce S (entropy)

System dynamics----- (had enough yet?)

Open system: stuff comes in, goes out, e.g. energy

Closed system: everything stays in e.g. mass

Steady state: balance of inputs and outputs (money example)

Feedback: think of the howling speakers at assembly: microphone picks up the speaker, gets louder, goes on and on: positive feedback

Positive feedback: response makes the situation stronger/unstable: capsizing ships, childbirth, bleeding to death, climate change, melting permafrost, albedo decrease in the arctic...

Negative feedback: response makes the situation more stable, tends towards recovery: stable ships at sea, sweating, good relationships

Questions:

1. Explain the difference between energy and power
2. UV radiation will cause sunburns but infrared will not. Why?
3. What are the 3 laws of thermodynamics?
4. Give an example of positive and negative feedback