perpetual motion

[jerryyu]

how does perpetual motion defied the law of physic and the law of thermodynamic?

[TonyMcC]

For every machine there is an input power and an output power. Because of losses in the machine the output power will always be less than the input power. This is known as less than 100 percent efficiency. So it is no use trying to use the output power to drive the machine. Usually the losses in the machine can be detected as a rise in temperature.

[StringJunky]

For every machine there is an input power and an output power. Because of losses in the machine the output power will always be less than the input power. This is known as less than 100 percent efficiency. So it is no use trying to use the output power to drive the machine. Usually the losses in the machine can be detected as a rise in temperature.

 

I think also, even if you could make a perfectly efficient self-sustaining closed loop system where output equals input the instant you try to connect something to it to use some of the energy the efficiency will drop below perfect and you have to top it up with more energy because you are moving the energy ouside of the loop so you could never make a useful machine that is also self-sustaining.

Edited October 16, 2010 by StringJunky

[jerryyu]

what is a closed loop system?

 

For every machine there is an input power and an output power. Because of losses in the machine the output power will always be less than the input power. This is known as less than 100 percent efficiency. So it is no use trying to use the output power to drive the machine. Usually the losses in the machine can be detected as a rise in temperature.

 

how about a transformer? It created more output energy since the increased voltages resulted in more amps( though the energy will be lost at a faster rate due to higher resistance).

[swansont]

 

how about a transformer? It created more output energy since the increased voltages resulted in more amps( though the energy will be lost at a faster rate due to higher resistance).

 

A transformer increases voltage by decreasing the current. IV is constant (in an ideal system)

[jerryyu]

wait... voltage equals IR. By decreasing I, you will get less voltages. Or do you mean that a transformer increases the volts by decreasing the current and increases the resistances. So basically by increasing the voltages only the resistances is changing?

[StringJunky]

what is a closed loop system?

 

Where no additional energy is added to keep the system going...it powers itself.

[Spyman]

wait... voltage equals IR. By decreasing I, you will get less voltages. Or do you mean that a transformer increases the volts by decreasing the current and increases the resistances. So basically by increasing the voltages only the resistances is changing?

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.

 

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (V_S) is in proportion to the primary voltage (V_P), and is given by the ratio of the number of turns in the secondary (N_S) to the number of turns in the primary (N_P) as follows:

[math]\frac{V_S}{V_P}=\frac{N_S}{N_P}[/math]

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making N_S greater than N_P, or "stepped down" by making N_S less than N_P.

 

Energy losses

An ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%.

http://en.wikipedia.org/wiki/Transformer

[swansont]

wait... voltage equals IR. By decreasing I, you will get less voltages. Or do you mean that a transformer increases the volts by decreasing the current and increases the resistances. So basically by increasing the voltages only the resistances is changing?

 

V=IR in a resistive circuit; you can replace R with the impedance and it will hold in each winding of the transformer with the transformer itself being an inductive load. But across the two, you use conservation of energy: P=IV

[jerryyu]

I think also, even if you could make a perfectly efficient self-sustaining closed loop system where output equals input the instant you try to connect something to it to use some of the energy the efficiency will drop below perfect and you have to top it up with more energy because you are moving the energy ouside of the loop so you could never make a useful machine that is also self-sustaining.

 

But is it possible to make a perfectly efficient self-sustaining closed loop system where output equals input? (let just say you don't connect it to anything.)

[Spyman]

Sure, all you have to do is to completely remove friction and totally shield off gravity... B)

 

Perpetual motion devices are physically impossible in terms of our current understanding of the laws of physics.

 

"There is an undisputed scientific consensus that perpetual motion violates either the first law of thermodynamics, the second law of thermodynamics, or both."

http://en.wikipedia.org/wiki/Perpetual_motion

[swansont]

Gravity is a conservative force, so that's not a problem.

[Spyman]

Gravity is a conservative force, so that's not a problem.

Does not gravitational interactions predicted from general relativity, like gravitational waves or frame dragging, remove energy from the system?

[swansont]

Does not gravitational interactions predicted from general relativity, like gravitational waves or frame dragging, remove energy from the system?

 

I was debating whether I should have parenthetically included that caveat "classically" in my post. I should have. Conservation of energy is different in GR; in any locally flat frame, AFAIK, energy is conserved. The problem is in moving to other frames, since energy is not an invariant quantity.

 

From a practical standpoint, gravity is not the stumbling block to creating perpetual motion. Nature conspires against anyone creating a system with multiple nondegenerate energy states.

[jerryyu]

V=IR in a resistive circuit; you can replace R with the impedance and it will hold in each winding of the transformer with the transformer itself being an inductive load. But across the two, you use conservation of energy: P=IV

 

sorry but what is impedance?

[swansont]

sorry but what is impedance?

 

Impedance is like resistance, but includes the effects of capacitors and inductors, whose effect appear when there is time-dependent current. Inductive impedence varies with the frequency and capacitive impedance varies inversely with it.

[dragonstar57]

Impedance is like resistance, but includes the effects of capacitors and inductors, whose effect appear when there is time-dependent current. Inductive impedence varies with the frequency and capacitive impedance varies inversely with it.

is a plaint (or anything else) in orbit perceptual motion?

Edited February 2, 2011 by dragonstar57

[swansont]

is a plaint (or anything else) in orbit perceptual motion?

 

No. Planetary orbits will decay over time. (Assuming you meant planets and perpetual)

[dragonstar57]

No. Planetary orbits will decay over time. (Assuming you meant planets and perpetual)

yeah i did mean planets and perpetual thankyou for correcting the error.

so do orbits decay until the object collides with what it is orbiting?

ie. the moon will hit the earth and the earth will slowly spiral into the sun?

[swansont]

Right now the moon is receding from the earth (robbing us of rotational kinetic energy), but eventually that would happen if the sun were to live long enough.

[dragonstar57]

Right now the moon is receding from the earth (robbing us of rotational kinetic energy), but eventually that would happen if the sun were to live long enough.

does that mean that the moon is falling or does it mean that it is slowing the rotation of the earth?

[swansont]

does that mean that the moon is falling or does it mean that it is slowing the rotation of the earth?

 

Slowing the rotation rate of the earth.