Magnets to create Perpetual Motions Machines, Why is it Impossible?

[Deleted]

I'm not going to quote all the guys this applied to, so hopefully they'll see this.

Sure energy will always be lost in heat (electricity tunning through a wire makes it hot for example) or friction (anything spinning or moving). Even in space when the energy lost would be reeallly small. But for the sake of simplicity lets just look at it positively, and discuss if magnets can make a (almost) efficient machine.

 

[Deleted]

I only have a 12th grade level of physics education so keep that in mind. I was thinking about how energy cannot be created, and how magnets seem to break this rule.

If a bigger magnet pulls a metal object, it has done work on the object. But did the big magnet "lose" some of its magnetic power? No, right? So doesn't that mean magnets can do work forever (or until they wear out, if they do)?

Anyone who's a physics nut care to explain why we haven't gotten something like this invented yet? Using magnets to spin something would create friction in some way or another, but if the only loss of energy is through friction would it mean tis pretty damn efficient? And for all intents and and purposes is a very good machine for making energy?

I guess the problem is keeping the metal object from reaching the magnet, since then the "energy" will stop?

http://knowyourmeme.com/memes/troll-sciencetroll-physics

I think that about sums it up. IT'S TOO DAMN SIMPLE. And awesome.

OT: friction can be a *****.

Lol. This troll science stuff is pretty funny.

but...

Why doesn't this work?

I think its surface tension that allows a drop of water (the size of a basic straw is around that of a drop) to hold its shape and cling to the walls.

When using big bodies of water, the surface tension is not nearly strong enough to keep it all up, so it'll fall with some drops still on the sides of the giant glass tube.

 

[Eclectic Dreck]

Oh okay, thanks for clearing that up for me. What I basically read is this: The fact that both of them are stuck keeps them from moving the cart. That actually makes sense. However, does that mean if I were to make a car basically like that but where I could make the anvil move back and fourth repeatedly, would that make it move?

No, for the cart to move you have to apply a force on the cart that did not originate on the cart. Your example would have two of these forces. First, the friction between the anvil and the cart and then, when the anvil reached the end of the track. Both are functionally identical to the original example.

 

[cheywoodward]

If you don't know already skip to 1:50 into the song.

 

[robakerson]

The basic principle of using magnets to move things is currently used in *every* electrical motor and generator on the power grid...
So, yes, you're right, it's an efficient system for -converting- energy.

However, I entreat you to think of your original question in a new way.
Take a large planetary body, such as Earth, does Earth lose its gravity when objects fall towards it? No... Why can't we use the gravity to create perpetual motion (or 'free energy')?

Anything that falls towards earth is losing PE and converting it to KE. Once the conversion is complete, the only way to make the object move again (by the same gravitational force) is to insert energy into the system by moving it to a new position where it has more PE.

The same basic principle is at work in your example. At some point in the design you're going to hit a point at which the system requires an input of energy greater than the energy 'generated' by the simple interaction.


Also, the force of the magnet attracts the objects towards one another, which balances itself out. In as simple terms as I can think of, while the metal might be moving towards the magnet, the magnet is being 'pushed' towards the metal with the same amount of force.
This means that in the entire system (magnet + metal), no work is actually being done (without an input of energy from outside sources).

The only reason we can easily think of situations whereeither the magnet moves and the metal doesn't (Fridge magnets), or the other way around (your example) is because outside forces working on the system (Gravity, friction, etc).

 

[Hashime]

Because no system is 100% efficient. You may be able to fashion some sort of machine that can continue motion for a long time, but it will eventually stop, and no energy can be generated from the system.