Hot answers tagged

36 votes
Accepted

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 ...
NMech's user avatar
  • 24.3k
26 votes

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

Because it has the potential to produce mechanical work.
NMech's user avatar
  • 24.3k
20 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 ...
LShaver's user avatar
  • 449
19 votes
Accepted

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 ...
fred_dot_u's user avatar
  • 7,055
13 votes
Accepted

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}...
Dave Tweed's user avatar
  • 6,874
11 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 ...
NMech's user avatar
  • 24.3k
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 ...
Solar Mike's user avatar
  • 15.6k
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. ...
Rory Alsop's user avatar
7 votes
Accepted

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 ...
ChP's user avatar
  • 638
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 ...
manassehkatz-Moving 2 Codidact's user avatar
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 ...
sasguy's user avatar
  • 71
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 ...
R. Bourgeon's user avatar
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 ...
Fred's user avatar
  • 9,667
5 votes
Accepted

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 ...
NMech's user avatar
  • 24.3k
5 votes
Accepted

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 ...
NMech's user avatar
  • 24.3k
4 votes

Could Internal Ionisation Engine be a description of electric cars?

It's a very poor analogy, especially in presence of ion engines used for space travel, where the propellant is ionized inside the engine, then accelerated outwards. Besides, the electric cars are ...
SF.'s user avatar
  • 6,135
4 votes

4 Way Bugatti Tug of War

The force on each car is purely longitudinal because the restraining force of necessity runs thru the central point (origin). For example, the East and West forces cancel so far as the origin is ...
Carl Witthoft's user avatar
4 votes

Specific energy vs Specific power in batteries

Batteries can't deliver unlimited current. Internal resistance, and limitations of the chemical reaction within the battery make that it can only deliver so much current. And the more current is drawn,...
Bart's user avatar
  • 1,184
4 votes

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

If it worked he would not need the engine to maintain speed Ask your friend: If this is "perfect" — as you say — with no friction, no losses... then why do you need the engine to maintain ...
MichaelK's user avatar
  • 211
4 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.
Jeffrey J Weimer's user avatar
4 votes

Clutch role in a micro hydropower

The clutch provides an instant disconnect either for scheduled maintenance or in an emergency. If the water flow is stopped instantly, then the energy of that moving pipeful of water has to be ...
Solar Mike's user avatar
  • 15.6k
4 votes
Accepted

Question about flow temperature and storage temperature in a cogeneration plant

when the cogeneration plant switches of upon reaching 85°C flow and without another heat source, there's no way to reach 95°C. Are you sure the switch-off happens at 85°C flow, and not at 75°C return ...
mart's user avatar
  • 4,781
4 votes

How do 3 blade turbines come so close to the Betz Limit?

The Betz limit is based on an extremely crude model for an actuator disk. If you want to compare the performance of the product of a billion dollar industrial development program, let's at least use a ...
Phil Sweet's user avatar
  • 4,707
4 votes

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

The block in itself has no energy. If you build a kettle of water around it, the water will not heat up. If you attach axles to it, the axles will not suddenly start spinning. However, since we spent ...
Opifex's user avatar
  • 141
3 votes

Working hours of power plant generators

There isn't a single answer that covers large power plants around the world. There's way too much variation in generation plant, and way too much variation in the way that plant is used. Some plants ...
410 gone's user avatar
  • 3,751
3 votes
Accepted

How do I calculate the additional energy required to pump fluid through a restriction?

The pump power equation can be used to calculate the energy required in both scenarios. Convert the additional $\Delta P$ to head, then calculate the difference in required hydraulic pump power. Both ...
morristtu's user avatar
  • 538
3 votes
Accepted

Trying to understand how much it costs to run my clothes dryer

You measured one load to take 1.8 kWh. That implies that 7 loads would take 12.6 kWh. If these 7 loads are repeated 52 times per year, then a whole year of operating takes 655 kWh. As a sanity ...
Olin Lathrop's user avatar
  • 11.4k
3 votes
Accepted

How high will a flywheel catapult launch a payload?

This is a very interesting problem. Energy approach At first I was inclined to solve it though energy i.e.: $$\frac{1}{2}I_{fly}\omega_0^2 = \frac{1}{2}I_{fly}\omega_1^2 + \frac{1}{2}I_{lev}\omega_1^2 ...
NMech's user avatar
  • 24.3k
3 votes
Accepted

Converting between MMBTU and MWh

IMHO, the difference is that you are trying to compare different things. I'll try to sum it up in the following table: coal gas EPA 0.32 tCO2eq/MWh 0.181 tCO2eq/MWh e-control 0.880 tCO2eq/MWh 0.440 ...
NMech's user avatar
  • 24.3k
3 votes

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

Aside from the efficiency, the blades of wind turbines are basically a wing, aerofoil, the actual upwash and downwash zone are much greater than the wing's cross-section. If the blades are too close ...
kamran's user avatar
  • 22.2k

Only top scored, non community-wiki answers of a minimum length are eligible