Testing the TK Tar Baby

[Groundloop]

GL, as TK alludes in his post, that s² term isn't anything to do with the amount of time it takes to move the mass. It's a counter-intuitive artefact of the way these units are ultimately derived.



When I wind my watch, the amount of energy stored in the spring - the work done - is identical no matter whether I wind it at the rate of 1/4 turn per week, or in one frenzied burst.


I put a brick on one end of a see-saw, and a pail on the other. I run a hose into the pail. It doesn't matter whether I turn the tap on full, or it barely drips, by the time the brick has been raised, the same work has been done; the brick has the same additional potential energy - also measured in Joules - in each case.

mrsean2k,

I'm fully aware that you can use different time and get the same potential energy.

The Joule is not a timeless unit. And when talking about work done as Watt then
you have to use time. 1 Joule = (1A*1V)*1Sec. This is a Watt per Second.

You lifted the brick with a electric motor and did use 1 second to lift the brick 1 meter using 1 ampere at 1 volt.
You lifted the brick with and electric motor using a 1:10 gear and did use 10 seconds to lift the brick 1 meter using 0,1 ampere at 1 volt.

Same amount of energy used in both cases.

GL.

[mrsean2k]

GL, the problem remains that you are digging into the derivation of some units and not others.


You state Watts = Volts x Amps


Agreed.


But how is the Amp defined?


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


"In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time"

The Watt is, by definition inextricably linked to the concept of time.

A "Watt per second" isn't a Joule. "1 Watt" is by definition "1 Joule / second" (or "1 Joule per second" if you prefer)

Determining total work done or energy - by definition and necessity - involves multiplying the rate at which the work is done - measured in "Watts" or "Joules per second" - by the number of seconds, returning Joules. A quantity that exists independently of time.




But even if that still doesn't seem correct intuitively, consider a thought experiment; what if the total energy or work done *was* dependent on the time taken to do it? Where would that lead?


It would mean, for instance, that mechanical perpetual motion would be an everyday occurrence. We wouldn't need to mess around with batteries, function generators and mosfets. We'd just need a supply of bricks, and a lift. Lift the bricks slowly up one side, drop them down the other, harvesting the extra kinetic energy energy created when it hit the ground. And the slower the lift, the more free energy we'd have!

[mrsean2k]

mrsean2k,

I'm fully aware that you can use different time and get the same potential energy.

The Joule is not a timeless unit. And when talking about work done as Watt then
you have to use time. 1 Joule = (1A*1V)*1Sec. This is a Watt per Second.

You lifted the brick with a electric motor and did use 1 second to lift the brick 1 meter using 1 ampere at 1 volt.
You lifted the brick with and electric motor using a 1:10 gear and did use 10 seconds to lift the brick 1 meter using 0,1 ampere at 1 volt.

Same amount of energy used in both cases.

GL.

We're almost in violent agreement.

Your example is a perfect illustration.

What I can't understand is how you can reconcile:

    "The Joule is not a timeless unit"

with

    "Same amount of energy used in both cases"



I think it almost certainly has to do with a misapplication of the term "per" and what that does to understanding.


You say:

    "1 Joule = (1A*1V)*1Sec. This is a Watt per Second."

it isn't! In fact, that's a Watt-Second (total Watts * total Seconds),


And look what happens to the time element when this correction is made. Remember, 1 Amp is an amount of charge flowing past a fixed point *per second*.


So using CH to represent that amount of  charge and substituting:

    "1 Joule = ((CH / 1Sec) * 1V) * 1Sec"


The "1Sec" terms cancels out in the numerator and denominator and you're left with a value that's *independent* of time.

[Groundloop]

GL, the problem remains that you are digging into the derivation of some units and not others.


You state Watts = Volts x Amps


Agreed.


But how is the Amp defined?


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


"In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time"

The Watt is, by definition inextricably linked to the concept of time.

A "Watt per second" isn't a Joule. "1 Watt" is by definition "1 Joule / second" (or "1 Joule per second" if you prefer)

Determining total work done or energy - by definition and necessity - involves multiplying the rate at which the work is done - measured in "Watts" or "Joules per second" - by the number of seconds, returning Joules. A quantity that exists independently of time.




But even if that still doesn't seem correct intuitively, consider a thought experiment; what if the total energy or work done *was* dependent on the time taken to do it? Where would that lead?


It would mean, for instance, that mechanical perpetual motion would be an everyday occurrence. We wouldn't need to mess around with batteries, function generators and mosfets. We'd just need a supply of bricks, and a lift. Lift the bricks slowly up one side, drop them down the other, harvesting the extra kinetic energy energy created when it hit the ground. And the slower the lift, the more free energy we'd have!

mrsean2k,,

Great discussion. :-)

And how is volt defined?

A single volt is defined as the difference in electric potential across a wire when an electric current of one ampere dissipates one watt of power.

So, 6.241 × 1018 electrons traveling through a wire with current of one ampere dissipates one Watt of power.
That can also we described in the attached formulas.

So, 1 Ampere = 1*Coulomb/s and 1 Volt = J/Coulomb this gives W = Coulomb/s * J/Coulomb gives W = J*s

Wouldn't  you know it. :-) I was wrong! :-)

I retract all my statements about the Joule and humbly bend down into the dust.

GL.

[mrsean2k]

GL, hehe, no reason for that. Very useful discussion for me as well, thanks!