Science review: energy and power

https://elab.hpa.edu/apes/texts/fr3e/fr3e_ch2.pdf

Energy: 

• same as work
• don't care if it happens fast or slow, just lift the rocks
• calculate your mass in kg (lbs x 2.2)
• how high are the stairs? (meters)
• lifting your mass up the stairs is WORK: PE = mgh. (gravity is about 10 here)
• how much work did you do walking up the stairs?
• important: not how FAST you do it, just how MUCH you did

Energy flows, feedback

• energy terms: cal, kcal, Joule, kWh, BTU
• power terms: Watt, J/s, hp
• EM spectrum
• KE= 1/2mv^2 or 3/2kT (T is degrees Kelvin)
• PE = chemical bonds or mgh (height potential energy)
• ICE vs. hybrid vs. electric cars
• thermo 1: conservation
• thermo 2: efficiency
• thermo 3: entropy
• open and closed systems
• equilibrium, stability and steady states
• positive feedback loops
• negative feedback loops

Energy units:

We use the following units for energy:

• calories: the energy used to heat 1 gram of water 1 degree C (note small c)
• kcal: one thousand calories
• Cal: a single food calorie, equal to 1000 chemical calories (note big C)
• Joule: the work needed to move something 1 meter against a 1 Newton force (note caps for dead people)
• 1 cal = 4.18 Joules (good to know)
• kWh = one kiloWatt of power used for 1 hour (heating tea for an hour, costs about $0.40 here)
• BTU: British thermal unit, most often seen in heating, ventilation and cooling (HVAC) systems

Power units:

• Watt: one joule every second
• kiloWatt: a thousand of those
• horsepower: 747 Watts

• 50 kg person, 10 m stairs, g = 10, equals 5000 Joules
  
• If you do this in 100 seconds, you have done this with 50 Watts of power (50 joules/second)
  
• If you did it in 10 seconds, you would be creating 500 Watts of power (that's a lot)
  
• 1 horsepower (hp) is 747 Watts
  
• Fun fact: some elite cyclists can create over 1000 Watts for many minutes-true animals
  
• Another fun fact: the electric company does not care how fast you use energy (kiloWatts), they only care how many hours you used this power (kWh)
  
• Think of water: you are not charged for how FAST you use the water, just how MUCH you use

Spectrum means a spread of values, so a musical spectrum might mean the lowest and highest notes you could sing or hear.

The electromagnetic (EM) spectrum describes EM radiation, that includes in order of increasing energy:

• radio waves: (radios use these)
• heat (IR or infrared): snakes can see these, also heat lamps over food or for people
• visible light: you can see these: ROYGBIV
• UV (ultraviolet) light: bees can see these, they also burn your skin
• X-rays: films and sensors can see these, they go through your skin, but less so through your bones
• gamma rays: go through most stuff (remember?), mutate DNA
• and cosmic rays: mysterious stuff, comes from supernova explosions, can form muons (cow rays)
• if you see Tiffany, ask her about relativistic muons...

The visible spectrum includes the following colors, in order of energy:

Low energy-------

• red
• orange
• yellow
• green
• blue
• indigo
• violet

You can now see why infrared is below red, and ultraviolet is above violet

Plant pigments have evolved to resonate with certain colors, like chlorophyll likes green light, others like reds and so on.

Fun fact: autumn leaves are red because the green is gone (winter, darker). The red was there all along.

Kinetic energy:

• When you ask a physicist (I am one, so I know) about Kinetic energy, they will drone on about moving objects, their mass and velocity...
  
• KE = 1/2mv^2
  
• This is incredibly fascinating you will agree (?) and it explains why car crashes at 80 mph are 4x more damaging than ones at 40 mph...
  
• In chemistry, we use KE to describe the energy of moving molecules: KE = 3/2kT, where T is the absolute temperature (Kelvin)
  
• This means that if you double the Kelvin temperature, you double the KE of a molecule.
  
• This changes for different molecule shapes (3 comes from x, y, z motion), which you may find interesting if you study physical chemistry (ask Dr. J)
  
• For our purposes, we need to know that increasing temperature increases the speed of molecules:
  
• 3/2kT = 1/2mv^2
  
• So, those physics guys were not crazy.
  
• This has huge implications on climate change, phase changes, rain, condensation, and many other things.
  

Potential energy:

• If you ask a physicist (what, again?) about potential energy, they will blather on about mass, gravity and height.
  
• While scintillating, this is useless in most chemical equations, which tend to happen at the same height.
  
• It does, however impact some weather phenomena, so let's let them have this one.
  
• If you ask a chemist about PE, they will often refer to chemical bonds, which represent energy stored like a spring holding molecules together
  
• If you ask a nutritionist about PE, they will talk about Caloric content (food)
  
• If you ask a coach about PE, they will tell you about the untapped potential of an athlete...maybe
  
• In APES, we mainly care about stored energy, usually in a phase change (latent heat of vaporization) or chemical bonds like in food.
  

ICE, hybrid and electric cars:

• ICE stands for internal combustion engine (e.g. normal cars, lots of heat, hot brakes etc.)
• hybrid cars capture the KE of motion and store it in batteries to accelerate the car, saving energy
• electric cars do this as well, but have no thermal engine parts like ICE or hybrid cars, so they are much more efficient
• electric cars capture braking kinetic energy and store it as chemical energy in batteries (often lithium)

Thermodynamics: one two and three

Thermodynamics is the study of heat (thermo) in motion (dynamics)

There are three big laws of thermodynamics:

1. you cannot create or destroy energy (you can't do this with mass either, more on this later)
2. in any reaction, there is an energy "tax" you could think of as friction
3. all reactions go naturally towards disorder

• You can imagine a magical car that you put 1000J of energy in the tank and 2000J of work is done by the engine.
  
• No
  
• Way.
  
• The most efficient Formula one racing car engine is about 50% efficient.
  
• Where does the rest go?
  
• Heat.
  
• Your body is at most 33% efficient in turning M&Ms into work. The rest?
  
• Heat.
  
• One way of looking at disorder is entropy, a measure of disorder.
  
• You can imagine a pool table, hitting the triangle of balls and then spreading across the table.
  
• It is more likely to go in this direction (more disorder) than to have the balls spontaneously jump out of the pockets and form a perfect triangle.
  
• Not to get depressing, but there is a formula that goes like this:
  
• ∆S for the universe is >0 translation: the universe always moves towards disorder
  
• so sad...
  

Open and closed systems:

• This means different things to different folks, but you could imagine a system where mass and energy are contained in the system as closed.
  
• You might also look at a system where certain nutrients are recycled as closed.
  
• You could look at recycling paper as a closed system to a degree.
  
• Most of our product cycles are open: we throw stuff away instead of recycling.
  
• Much more on this later...
  

Equilibrium, stability and steady states:

• Equilibrium means literally "equal freedom" , in this case equal freedom to move from one condition to another.
  
• Imagine two fish tanks with a pipe connecting them.
  
• Fish are free to move from one to the other.
  
• Not the same fish, but about the same fish on each side.
  
• This is equilibrium.
  
• Stable systems are ones where equilibrium exists, and can recover from stresses (resilience)
  
• Steady state systems are ones where the inputs equal the outputs, and are usually stable as well.
  
• Unstable systems have nasty feedback loops (see below)
  

Positive feedback loops:

• In a positive feedback loop, any change causes a greater change as a result
  
• Boat example: if a large cruise ship tilts over, the mass of the people on the ship make the ship want to tilt more.
  
• Climate change example: as the planet warms, ice sheets melt, changing from reflective ice to darker ocean water that absorbs more heat, melting more ice.
  
• Permafrost example: as the planet warms, the permafrost melts, releasing methane gas, which is a greenhouse gas, causing more warming, and more methane...
  
• Positive feedback loops exist in your body as well: massive blood loss and childbirth are two examples.
  

Negative feedback loops:

• Where positive feedback tends towards instability, negative feedback loops restore stability, and naturally recover to initial conditions.
  
• As you exercise, your body sweats, cooling the body.
  
• This is a negative feedback loop.
  
• Some coast guard rescue boats are created with negative feedback as well: the more they tip over, the more they want to come back to normal.
  
• Psychologists often use these terms to describe personalities and relationships...
  

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