Stupid question alert - magnets
Discussion
Hi all. Apologies in advance of the stupid question, but my 9 year old has 'discovered' magnets and asked a question I can't really answer so thought I'd come on here and get a decent reply to him!
Basically he's learning about wind turbines and asked why they cannot use magnets to repel and get them to turn? He also found this video https://www.youtube.com/watch?v=jiAhiu6UqXQ to prove his point, just on a much bigger scale.
Help......I can't come up with a sensible argument other than magnets lose their power quickly! Which I know is probably a daft answer to give him.
Basically he's learning about wind turbines and asked why they cannot use magnets to repel and get them to turn? He also found this video https://www.youtube.com/watch?v=jiAhiu6UqXQ to prove his point, just on a much bigger scale.
Help......I can't come up with a sensible argument other than magnets lose their power quickly! Which I know is probably a daft answer to give him.
For a magnetic to repel, it must first get into the magnetic field that causes it to repel. This takes energy. You cannot move a magnet into a repeling field without using energy. The energy it takes to get into the field is the most you will ever get back out of the system.
His hand adds the additional energy at the start to get it moving. He is just pushing the fan indirectly via a magnetic force. When his hand stops moving, the magnets might as well not be there. The fan just slows down based on the quality of the bearings.
His hand adds the additional energy at the start to get it moving. He is just pushing the fan indirectly via a magnetic force. When his hand stops moving, the magnets might as well not be there. The fan just slows down based on the quality of the bearings.
audi321 said:
Hi all. Apologies in advance of the stupid question, but my 9 year old has 'discovered' magnets and asked a question I can't really answer so thought I'd come on here and get a decent reply to him!
Basically he's learning about wind turbines and asked why they cannot use magnets to repel and get them to turn? He also found this video https://www.youtube.com/watch?v=jiAhiu6UqXQ to prove his point, just on a much bigger scale.
Help......I can't come up with a sensible argument other than magnets lose their power quickly! Which I know is probably a daft answer to give him.
That video is essentially a 'perpetual motion machine', there are lots of these, they are all fakes because you cannot beat physics. Energy cannot be created or destroyed, only converted from one form to another.Basically he's learning about wind turbines and asked why they cannot use magnets to repel and get them to turn? He also found this video https://www.youtube.com/watch?v=jiAhiu6UqXQ to prove his point, just on a much bigger scale.
Help......I can't come up with a sensible argument other than magnets lose their power quickly! Which I know is probably a daft answer to give him.
https://www.youtube.com/watch?v=g4tO0kBOzqk
MikeStroud said:
4x4Tyke said:
Energy cannot be created or destroyed, only converted from one form to another.
I too was taught that at school.But also I thought mass could be converted to energy? As in E=mc^2 i.e. energy can be created from mass.
What am I missing here?
We do have entropy though so some forms of energy are less useful than others and it all tends downwards towards heat.
So explain to the kid you cant get energy out that isnt already in, and you never get out 100% because you always loose some to heat etc.
You've really answered your own question - permanent magnets lose their magnetism when exposed to other magnetic fields. The "fan generator" in the video will work until the magnets become too weak to overcome the friction present in the bearings and air resistance (it would be more efficient if the blades were flat). This is the reason why electromagnets are used is applications where a constant magnetic field is required.
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