Sustainable Energy class notes

In-class group exercise: Improvising from any material you like, make a pendulum with the longest period you can manage.

Minimizing the weight and surface area of the string
Maximizing the weight while minimizing the surface area of the weight (eg a sphere)
Maximizing the weight and the drop height (string length)

The winning pendulum (eg the piece that swung for the longest period of time) was the heaviest weight (with a high drop point). Despite the lack of aerodynamics (we used a thick string and a bulky pipe fitting), it so massively heavy that it started with huge potential energy compared to the others. It remained in motion for over 30 min.

Discussion: what are the forces here?
Gravity – causing mass to accelerate downwards
Friction – slowly reducing the acceleration of the mass

What kind of energy is being converted?
Potential converting to kinetic, converting back to potential
Kinetic to thermal heat loss (impacting air molecules, transfer of kinetic energy)

Foucalt's Pendulum

Foucalt’s pendulum has a very long period, long enough for the earth to noticeably rotate beneath it. It is made with a very heavy bob on a very long string.

What’s the difference between Force, Energy, and Power?
Force is the way energy is transfered/used/transformed inside a system – measured in (J)oules
Power is the RATE force is applied to the system – measure in Joules/time
Energy is the QUANTITY of force applied over a specific distance/time – measure as (rate)*(span) – (J/time) * time = J

Isn’t energy the same thing as work?
Work presumes that the force is being applied to accomplish some goal. If not, avoid calling it work.

What’s the difference between heat and energy?
Heat is a specific form of energy, the excitation of molecules. Fast-moving molecules tend to take up more space than slow ones, which is why things expand as they get warm. When temperature is a factor in an equation, it tells us about one form of energy in a system. Interesting things happen when the energy gets really really low (77 Kelvin for example).

This course is about conservation of energy. Why is this difficult?
Energy as we refer to it is a concentrated (ordered) form that can be easily moved between systems, allowing us to accomplish specific goals. However, every time we use energy, it finishes in a less ordered form Once disordered, more energy is required to gather it into useful form again.

Well, there goes the universe

Someday, this disorder (entropy) will so completely disperse energy in the universe that it can no longer be reordered or transformed – we envision this as the absolute heat death of the universe.

What kinds of forces are there in the universe?
At the atomic level, the main forces are the binding forces and an exchanging force: the binding forces are nuclear strong (N), electromagnetism (EM), and gravitational (G) and the exchanging force is nuclear weak. All other forces on a macroscale arise from these basic forces.

N: Nuclear strong holds quarks together to form protons and neutrons, and binds protons and neutrons inside the nucleus
EM: electromagnetism, attraction of unlike charges and repulsion of like charges
G: gravitational, the attraction between masses across a distance
Nuclear weak: sub-atomic particles change “flavour”, resulting in fusion or radioactive decay
Chemical (EM – binding and repulsion between atoms)
Thermal (EM – atoms hitting atoms, transfer of kinetic energy)
KineticGravitational (G – moving matter)
Radiation (nuclear weak – changing matter – eg a neutron’s down-down-up becomes a down-up-up (a proton), emitting an electron and anti-electron neutrino in the process).

*Note: Later, EM and nuclear weak were found to be aspects of the same force, now called Electro-weak. I personally find that confusing, so I prefer the four-force model.


Bonus question: What’s an example of chemical energy converting to electromagnetic energy?

Firefly (copyright Animal Planet)

Fishermen haul in nets of firefly squid

1. Chemi/bioluminescense: Excited electrons release photons, i.e. electromagnetic radiation

Warning: I can shoot lightning from my stomach

2. Bioelectrogenesis: Electric eels generate an ion cascade that reverses the charge of special muscle-like cells, creating a voltage gap. It can discharge up to 1 Amp and 500 Volts, enough to kill a human.

Super bonus question: Chlorophyll is a way to convert light energy to chemical energy. It uses CO2 and water and produces O2 as waste (the O2 is released from water via hydrolysis). How does the energy act on the carbon product? Where does it go?

Carbon is smashed together into chains (“carbon fixation”), which form plant tissue (cellulose) and plant food (starches, sugars). In other words, plants filter carbon from the air to increase their mass. This is non-intuitive to humans, since we do not think of air as a source of nutrition. Our oxygen fixation is temporary – we do not build with it.


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