Perpetual motion

[matty2670]

I know this one keeps cropping up, but I'm new to AB so bear with me... If I connect a rechargeable battery to an electric motor, which then powers a dynamo connected to the battery, will this set up keep running indefinitely? Does this in fact fall into the remit of perpetual motion? Why don't I just buy the bits from Maplin and build one to find out? Should I get out more?

[Hammer]

It won't work because the charge put back into the battery will be less than the charge taken out. Sooner or later the battery will run flat.

[Space]

of course it won't keep running indefinitely.
The battery, the motor and the dynamo all waste a part of the energy, so it will run out of energy and stop.

If you buy the bits from Maplin, have a look at the specifications, look for the efficiency of the components. You will find it's less than 100%, therefore it won't work.

[Clanad]

Personally, I think your last reflection has a great deal of merit. The single thing most people overlook of fail to consider when proposing perpetual motion machines is the simple Law of Conservation of Energy. This, along with its cousin, the First Law of Thermodynamics. A good reference says this:... the total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system. In other words, energy can be converted from one form to another, but it cannot be created or destroyed.
Your proposed electric motor is a thermodynamic unit... i.e., it consumes energy, does work and in the process emits heat, as does the dynamo. In each case energy is lost by its transistion or changing into heat. Over a period of time this, and resistance in the form of friction, would stop your machine. Probably wouldn't take very long, actually...

[logman]

Attach a solar panel as a back up, to kick in when the battery gets low, and i think you'v got it made

[JudgeJ]

Until dusk, or until the Sun runs out of hydrogen fuel!

[LCBoman]

Regarding the idea of a solar panel - that would mean it is not a perpetual motion machine as you are constantly adding more energy. Although I appreciate that the answer probably wasn't particularly serious in the first place!

[matty2670]

Thanks to all of you for taking the time to reply. I may not have a grasp of basic physics, but I AM intelligent enough for the thinly veiled insults and sarcasm not to be lost on me..! Who would have thought that from the hallowed halls of learning could spew forth such bitter bile... Never fear, I will have a few cans of Special Brew tonight and think of something else to ask tomorrow. Farewell.

[Clanad]

Hey! I for one was simply concurring with a question you asked... "Should you get out more?"... seemed a reasonable conclusion at the time... no bile, insults or sarcasm intended though... Perhaps you shouldn't get out more? ...

[matty2670]

Sorry Clanad, no offence intended! I was only joking. I am genuinely grateful to anyone who takes the time to post an answer. But, and this isn't aimed at anyone here, I do get a bit annoyed with the replies to some posts by people who try to belittle the person asking the question. Sure, to an expert in the relevant field the things I ask might seem trivial, but if I didn't want to know the answer, I wouldn't ask! Surely this forum is all about improving our knowledge, even sometimes by an infinitesimal amount, but having fun in the process! Right, now I'll put my handbag down. That little rant has given me quite a headache. Thanks again folks!!!

[joko]

matty - are we reading the same thread? I can't see any insults, sarcasm, bitter bile or belittling... can you point them out? genuinely confused...

[mibn2cweus]

Could it be a case of excessive monitor glare?

[matty2670]

Joko: the clue is in the bit that reads '"this isn't aimed at anyone here." Blimey, you lot don't half take this seriously. (But only in the science sectin, it seems...)