Energy and the "Power" of back of the envelope calculations.

First, to discuss Energy and Power we need to define them. Johannes has repeatedly confused power and energy and other units- when

this is pointed out to him he acts as if its an unimportant matter of semantics. IT ISN'T! In order to converse about these terms, you MUST understand the meaning of these terms. The words have real, well defined, meaning.

ENERGY

One way to define energy is as a force, F, applied over a distance (in meters, m), d: E=F*d. Since force equals Mass(kg)*Acceleration(m/s2) energy has units of kg*(m/s2)*m, or Joules.

Energy has many different forms, the key thing to remember is that energy is always conserved. Take, for example, a drop of water falling from the faucet into a pool of water. The drop starts off at 'rest' with gravitational potential energy. As it falls this gravitational potential energy is converted into kinetic energy, in turn some of this kinetic energy is transferred to the atoms in the air through which the drop falls. When the drop hits the pool kinetic energy is transferred to air and water molecules to produce sound waves and water waves, and eventually the kinetic energy is distributed among the atoms in the system and becomes thermal energy.

The energy of the system before and after is the same, only the form has changed. When you increase the temperature of a substance you are increasing the average kinetic energy of the atoms in that substance. Hydroelectric dams use the Gravitational potential energy of water- kinetic energy of falling water turns turbines which in turn generate electrical energy which gives kinetic energy to electrons in wires, which then collide with atoms in the filament of your light bulb increasing their thermal energy causing them to radiate energy in the form of photons which in turn heat their surroundings.

Nuclear power plants are not that much different. Fission releases nuclear binding energy, this energy is mostly released in the form of the kinetic energy of nuclear particles. These particles collide, transferring kinetic energy to other atoms, and causing further fission events. This heats the atoms in the fuel, this heat is transferred to water atoms to make steam to drive the turbines that generate electrical energy...etc etc. There is NOTHING magic about the energy from nuclear fission.

The end result is what we call heat.

The ENERGY released by the Hiroshima bomb was the equivalent of ~20,000 tons (20 kilotons) of TNT. One kiloton is defined to be ~4.2*1012 Joules, so the energy released by the Hiroshima bomb was ~8.4*1013 (84 thousand billion) Joules.

Another useful way to express energy is in terms of the electron Volt- eV. 1eV=1.6*10-19 Joules or 1.6* (ten-billion-billionths of a Joule).

POWER

Power is energy per unit time, or Joules per second, or Watts. The energy delivered by running a 100 Watt light bulb for 27,000 years, and the energy delivered by the Hiroshima bomb is about the same- the difference is in the rate that that energy is delivered, or the power. The same energy can light a room for 27,000 years, or destroy a city depending on the rate its delivered.

Clearly the difference in meaning of the words 'energy' and 'power' is important.

Another important concept is the relationship between mass and energy. When you burn a candle, or detonate an atomic bomb mass is being turned into energy. In the Hiroshima bomb 64,000 grams of U235 underwent fission. Part of the mass of an atom of U235 is the nuclear binding energy. When it undergoes fission some of this mass/energy is released as explained above. The Hiroshima bomb turned a little less than 1 gram of mass into energy, roughly 1 part in 64,000 of the original mass of fissile material. A gram is about the mass of a dollar bill.

Everyone is familiar with the equation E=mc2 this equation gives the energy equivalent of a mass 'm' (c is the speed of light in a vacuum, ~300,000,000 m/s. The energy you get from converting 1kg of matter into energy is E=(1kg)*(300,000,000 m/s)2=9*1016kg*m2/s2= 90 million billion Joules. THIS IS THE MOST energy you can get from 1 kg of ANYTHING! The amount of energy we get from fission of U235 in a nuclear reactor is MUCH less than this amount- 1 kg of U235 gives us ~7.7*1013 Joules (http://en.wikipedia.org/wiki/Energy_density)

Scale

The energy of a drop of water falling is very small, but the energy of a billion billion 'drops' falling is considerable. The problem is Johannes does not seem to be able to distinguish between a drop, and Niagra Falls. Somehow Johannes has convinced himself that nuclear power is heating the world, causing our atmosphere and water to evaporate.

The power generation of the human race is estimated to be ~12 trillion (trillion =1000 billion) Watts, of this only ~1 trillion Watts is from nuclear power. This means we generate ~12 trillion (1.2*1013) Joules per second for consumption.

Elsewhere in this thread I did a simple back of the envelope calculation showing that if ALL this power went into heating the oceans for a full year (neglecting the fact that most of it would be radiated out to space) that it would only heat the oceans by .000066 degrees. Johannes ignored this calculation and rambled something about there being ~1000 tons of U235 in nuclear power plants around the world as if this changed the facts in any way. It changes nothing.

Just for kicks, lets pretend we could turn 1000 tons of U235 into pure energy - %100 matter energy conversion (VERY unrealistic, we cant even get 1/1000 of that). The MOST energy possible to get from 1kg of ANYTHING is

9*1016kg*m2/s2= 90 million billion Joules=9*1016Joules. So 1000 tons (1 million kg) gives us E1000 tons=9*1022Joules. Please remember this is FAR more than the most energy we can possibly extract from U235, by several orders of magnitude.

If ALL this energy went to heating the oceans how much warmer would the oceans be?

E1000tons=DeltaTocean*CWater*MassOceans. Using E1000tons=9*1022Joules and the heat capacity of water CWater=4.2*103J/(kg*degree), and the mass of the world's oceans MassOceans=1.4*1021kg and solving for DeltaTocean gives us a temperature increase of about 1.5*10-2 degrees or .015 degrees. This assumes that everything, the original fuel, and the speen fuel releases the MAXIMUM possible energy.

So, you can see that even if we make ridiculous assumptions that throw the numbers MANY orders of magnitude in Johannes favor we still get a ridiculously small number. I wouldnt even classify his rantings as pseudoscience- they are just absolute, pathetic, gibberish. Remember, we are assuming that you can get more than 1000 times the energy from U235 than what we actually get- that alone made the answer we got over 1000 times too large.

Dont worry, nuclear power is not heating the world, it is not causing our water and atmosphere to evaporate.

People like Johannes and SDAI think that by throwing around scientific terms that they can sound like they actually know what they are talking about.... but it really only takes a little education to see they are just full of crap.

Dont take them seriously.