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36 votes
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How does turning off electric appliances save energy

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is ...
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26 votes

Why does "potential energy" have the word "potential" in it?

Because it has the potential to produce mechanical work.
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19 votes

How does turning off electric appliances save energy

Timescales on the grid Power demand fluctations can be broken into timescales from micro-seconds to decades. On the "decades" end of the scale, the power industry and utility regulators work ...
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19 votes
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Why does "potential energy" have the word "potential" in it?

potential (adj.) Capable of being but not yet in existence; latent or undeveloped. The block is stationary and therefore not performing work. If the block never moves, the potential energy remains ...
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15 votes
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What is the most efficient means of warming a building with a high ceiling?

Your question sort of has two parts: How to supply heat, and how to keep it in. Large open rooms with a high ceilings are most efficiently warmed with radiant ceiling heat. Warm air rises, which ...
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14 votes

Can the Sabatier reaction power a vehicle?

According to Wikipedia: It [Sabatier reaction ] involves the reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures in the presence of a nickel ...
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12 votes
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Calculating torque needed to climb a graded hill

I think you're overcomplicating things. To push 85 kg up a 15% slope against gravity of 9.8 m/s2 requires a force of $$ \sin (\arctan (0.15) ) = 0.1483 \approx 0.15 $$ $$F = 85 kg \cdot 9.8 \frac{m}...
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10 votes

How can one calculate the change in heat energy when the specific heat varies with temperature?

In a similar vein to my answer about calculating the lever force in a continuous situation; you need to use integration. You start by taking the standard heat law that you are familiar with $$ \...
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10 votes

How does turning off electric appliances save energy

Yes, they monitor demand and due to differences in how different power stations are controlled they can increase or reduce output to match demand. Some power plants like nuclear run at full output as ...
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9 votes

Relationship between wind velocity, turbine rotor diameter, and power output

It's not a simple relationship. First let's deal with the kinetic energy of the wind passing through the rotor. The mass of air passing through it in one second, $m$, is equal to the the density of ...
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9 votes

Is the main goal for wind turbines to take maximum energy for a given diameter?

The function of the wind turbine is to extract as much as possible energy from the moving mass of air. The energy of a mass $m$ of air is $$KE = \frac{1}{2}m v^2$$ and the power is (because the mass ...
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8 votes

What is the most efficient means of warming a building with a high ceiling?

Another option to the radiant solution above would be under floor air distribution systems (UFAD) using displacement ventilation. These systems require a raised floor plenum which works well in ...
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7 votes
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What causes rechargeable batteries to age? What can be done to extend life of these batteries?

One of the problems that plagued older rechargeable batteries (e.g. Nickel Cadmium ($\text{NiCad}$) and Nickel Metal Hydride ($\text{NiMH}$)) was the memory effect. The memory effect occurs when a ...
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7 votes

Magnetic Entrapped Storage at 0 gravity

Flywheels are used in space, but not for storage of energy. They are used for attitude adjustment, as the spinning of a large mass has significant implications in an object which is free to move. ...
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7 votes
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Why can't energy be entirely recovered from a moving car's rotating wheels?

Get a small DC motor from a cheap toy or something and put a gear or a flywheel or something on the shaft to make it easy to spin with your fingers. You should find these in the toy as well. Ask your ...
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6 votes

Turning an engine over with engine compression

There is another reason for this in multi-cylinder engines. While one cylinder is compressing the air, another is decompressing it. The net result is that the torque as a function of position gets ...
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6 votes

How can one calculate the change in heat energy when the specific heat varies with temperature?

Neither. In this sort of situation, there's no "simple" linear solution; you need to use integral calculus to add up the incremental heat absorbed at each temperature along the way. The only time that ...
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6 votes

How does turning off electric appliances save energy

Peak Demand One of the biggest issues in the electricity business is managing peak demand. This is the maximum amount of electricity needed at any one time. Typically this will be the middle of the ...
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6 votes

Why does "potential energy" have the word "potential" in it?

In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, attachments, electrical charge, magnetic field, mass, etc., and ...
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5 votes

Is compressed air energy storage economically viable in the home?

It isn't completely infeasible. Just to get a ROM (rough order of magnitude), let's assume that a typical household that isn't using electricity for heating uses about 1 kW on average, and that you'd ...
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5 votes

Does The W*nkBand Work?

Because this question has proven a little more derisive than I had anticipated (where's that engineering sense of fun/humour?)- I thought I'd attempt an answer as well, if only to prove it's an ...
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5 votes

Working hours of power plant generators

Nuclear power plants are always working, except circa one month/year for maintenance. It's mainly because stopping the nuclear reaction and cooling the reactor down is a very long and difficult ...
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5 votes

Why can't energy be entirely recovered from a moving car's rotating wheels?

There are some people who cannot be told. They think they know everything and that they are never wrong. My advice is do not try to convince your friend that your friend is wrong. You will always lose ...
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5 votes

How to convert Joules(kinetic energy) plot chart into watts?

To convert a plot of J versus s to a plot of J/s vs s, take the derivative. Here is my quick-and-dirty answer after digitizing the data.
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5 votes
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What does MM prefix mean in MMtoe?

TL;DR: the MM in MMtoe is probably related to the Latin Numeral M (for 1000). In that context MM means one thousand thousands (i.e. one million) Although this is very confusing, the bottom line is ...
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5 votes
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What happens to generated electricity if it is not used?

TL;DR: a small portion of the excess energy is stored in the form of rotational kinetic energy, however, generator controls make it so these amounts are not significant. electricity generation (Al ...
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4 votes

What is the most efficient means of warming a building with a high ceiling?

Here are some ways to keep the warm air from escaping: Revolving doors prevent a constant stream of air exchange between the inside and outside. Air lock areas - a double-set of sliding doors can ...
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4 votes

How could we possibly harness the energy from the Earth's negative charge?

I think Failmond's first post does a solid job with the analysis. You have a voltage potential across a resistor(the air). You can not remove air from the equation as it is what is sourcing and ...
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