The Naked Scientists

The Naked Scientists Forum

Author Topic: Magnetism & Constant Motion - Renewable Energy  (Read 8860 times)

Offline mbosma

  • First timers
  • *
  • Posts: 5
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« on: 10/04/2008 17:54:45 »
Is it possible to use magnets to create a constantly rotating object? i.e. to turn a spindle and create electricity? If so, can we harness the earth's magnetic field to do so?


 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3818
  • Thanked: 19 times
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #1 on: 10/04/2008 18:29:48 »
No
 

Offline mbosma

  • First timers
  • *
  • Posts: 5
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #2 on: 10/04/2008 18:38:38 »
I wonder why this wonít work. We can use magnets and electric fields to levitate objects, why canít we use lots of magnets to force an object to move around in a circular motion? Donít magnets produce fields just like the earth, only on a smaller scaleÖ
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #3 on: 10/04/2008 19:23:40 »
I can use a shelf to hold an object up; levitations isn't that different. In order to make something move I need to supply energy to it. Of course, I can also use an arangement of coils and magnets to move something - it's called an electric motor.
 

Offline mbosma

  • First timers
  • *
  • Posts: 5
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #4 on: 10/04/2008 20:04:10 »
Can we replace the electrically charged arangement of coils with another field magnet?
 

lyner

  • Guest
Magnetism & Constant Motion - Renewable Energy
« Reply #5 on: 10/04/2008 21:32:45 »
Not if there is any energy transferred.
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3818
  • Thanked: 19 times
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #6 on: 10/04/2008 22:00:50 »
You can of course use the rotating spindle to interpose sheets of magnetic shielding materiel and generate rotation that way (this was first tried about 250 years ago), the only snag is that more power is adsorbed in moving the shields than is generated.
This can also be done with gravitational fields but the shields have to billions of light years thick!
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3818
  • Thanked: 19 times
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #7 on: 10/04/2008 22:07:53 »
In some pubs it is forbidden to discuss, religion, politics or football, it would be nice to have a forum where discussion of blackholes, relativity and perpetual motion machines was forbidden
 

Offline Supercryptid

  • Hero Member
  • *****
  • Posts: 606
    • View Profile
    • http://www.angelfire.com/sc2/Trunko
Magnetism & Constant Motion - Renewable Energy
« Reply #8 on: 11/04/2008 01:37:22 »
Even if you could harness the Earth's magnetic field, the resulting energy extraction would weaken the field.

Something from nothing = no.
 

lyner

  • Guest
Magnetism & Constant Motion - Renewable Energy
« Reply #9 on: 11/04/2008 20:25:42 »
Quote
harness the Earth's magnetic field
A field is not energy, remember.
 

Offline Supercryptid

  • Hero Member
  • *****
  • Posts: 606
    • View Profile
    • http://www.angelfire.com/sc2/Trunko
Magnetism & Constant Motion - Renewable Energy
« Reply #10 on: 15/04/2008 12:56:12 »
Quote
harness the Earth's magnetic field
A field is not energy, remember.
I'm aware of that. But you can get a field to do work in the right circumstances.
 

Offline mbosma

  • First timers
  • *
  • Posts: 5
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #11 on: 15/04/2008 13:03:06 »
So let me try to get this straight.

Any work created by a magnet to repel an object is transferred to that object (transfer of energy)? In this scenario, energy used in creating a magnet will be equal to the work extracted from the resulting magnetic field.
 

lyner

  • Guest
Magnetism & Constant Motion - Renewable Energy
« Reply #12 on: 15/04/2008 13:14:25 »
Just repelling doesn't represent work it would have to be moving the object. It's when a force is moved through a distance (in that direction) that work is done. I can lean against a wall all day and I haven't done any actual work on the wall so I don't need any energy.
To 'get work' out of field, you have to allow something to move within the field - changing its potential, e.g. the iron weight driving a grandfather clock going downwards. You would need to do the same amount of work (plus losses, of course) to get the iron back where it started from. The Earth's gravitational field remains the same throughout, supercryptid.
« Last Edit: 15/04/2008 13:20:44 by sophiecentaur »
 

Offline Supercryptid

  • Hero Member
  • *****
  • Posts: 606
    • View Profile
    • http://www.angelfire.com/sc2/Trunko
Magnetism & Constant Motion - Renewable Energy
« Reply #13 on: 15/04/2008 13:26:00 »
Just repelling doesn't represent work it would have to be moving the object. It's when a force is moved through a distance (in that direction) that work is done. I can lean against a wall all day and I haven't done any actual work on the wall so I don't need any energy.
To 'get work' out of field, you have to allow something to move within the field - changing its potential, e.g. the iron weight driving a grandfather clock going downwards. You would need to do the same amount of work (plus losses, of course) to get the iron back where it started from. The Earth's gravitational field remains the same throughout, supercryptid.
I'm not saying that you can get perpetual energy or anything. As you said, a field has to move something in order to do work. I can't just sit some magical extracter inside of a stationary field and suck energy out of it.
 

lyner

  • Guest
Magnetism & Constant Motion - Renewable Energy
« Reply #14 on: 15/04/2008 16:17:48 »
Yes, I now see what you were saying. If you charge up a capacitor, the field between the plates alters because you put energy in etc. etc..
 

Offline that mad man

  • Hero Member
  • *****
  • Posts: 724
    • View Profile
    • My music
Magnetism & Constant Motion - Renewable Energy
« Reply #15 on: 15/04/2008 16:22:17 »
Just repelling doesn't represent work it would have to be moving the object. It's when a force is moved through a distance (in that direction) that work is done. I can lean against a wall all day and I haven't done any actual work on the wall so I don't need any energy.

How does the equation work when you push against a wall expending energy and yet the wall does not move. I have just used up lots of energy pushing against a wall that does not move and yet there is no work done. How come, where does this used energy go or transfer to? Surely I must have done some work?

Sorry, I'm familiar with the work eq but I'm a bit confused on this one as it don't seem to work in this case, or does it?
What am I missing here?
 

Offline mbosma

  • First timers
  • *
  • Posts: 5
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #16 on: 15/04/2008 16:27:51 »
If 20 people push on a wall and it falls over, work is experienced. The ammount of work produced by one person is 1/20 of the total work. If one person pushes, work is experienced, but there is no physical result. It is transferred to the base of the wall/foundation, and the work has no long-term effect.
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3818
  • Thanked: 19 times
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #17 on: 15/04/2008 16:44:29 »
work is done when you use force to cause movement, this was day one of the physics course when I was at school.
The same applies when you use a source of voltage to push a current into a capacitor which then stores energy in propotion to its capacitance and the voltage squared.
« Last Edit: 15/04/2008 18:54:45 by syhprum »
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
Magnetism & Constant Motion - Renewable Energy
« Reply #18 on: 15/04/2008 17:13:29 »
Just repelling doesn't represent work it would have to be moving the object. It's when a force is moved through a distance (in that direction) that work is done. I can lean against a wall all day and I haven't done any actual work on the wall so I don't need any energy.

How does the equation work when you push against a wall expending energy and yet the wall does not move. I have just used up lots of energy pushing against a wall that does not move and yet there is no work done. How come, where does this used energy go or transfer to? Surely I must have done some work?

Sorry, I'm familiar with the work eq but I'm a bit confused on this one as it don't seem to work in this case, or does it?
What am I missing here?

Simply expending energy is not necessarily doing "work" in a physics sense.  As people have mentioned, work in physics only occurs when you move something using a force (Work=Force*Distance).  You can definitely expend a lot off energy in your body by pushing on something without moving it, but you won't be doing work in a physics sense.  In the case of pushing against a wall, your body basically gives off the energy as heat.
 

lyner

  • Guest
Magnetism & Constant Motion - Renewable Energy
« Reply #19 on: 15/04/2008 22:45:05 »
There is actually work done, in that example, because your muscle fibres take in turns to go taught and then relax (a force times a distance). The work is done on the inside of your muscles but not on the wall.
If 20 people can produce enough force to overcome static friction effects then they all get a chance to do some work. One on his own may not do any if he doesn't manage to move the wall at all.
Basic ideas of Physics are best kept to ideal cases or things tend to get out of hand unless you can use statistics.
 

The Naked Scientists Forum

Magnetism & Constant Motion - Renewable Energy
« Reply #19 on: 15/04/2008 22:45:05 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length