Magnetic motor (contradicts 2nd law of thermodynamic? )

[mathsTKK]

Hi, everyone ! I am a new member to PF but I find it helpful as people will give ideas and suggestions for me :)

Recently,I come across something called as a magnetic motor. From the design, a few permanent magnets are placed on the edge of a circular disk. Then, as another magnet approaches the disk, the disk spins due to the attraction between the magnet. Due to continuous magnetic attraction, the disk seems able to spin forever, like a perpetual motion machine. However, I realize that the 2nd law of thermodynamics does not allow perpetual motion. So, does the magnetic motor contradict with this law? Besides, I always come across the term ' free energy' which raises my doubt whether it's truly 'free'?

I hope that PF members can help me to clear my doubt. I am truly eager to know the physics and logic behind this contradiction.

Thank you everyone ^^

 

[Drakkith]

Welcome to PF! Unfortunately discussion of perpetual motion machines is not allowed here on PF due to the tendency for the discussions to get out of hand with crackpottery and nonsense. I will say that you have forgotten that when magnets attract each other they don't simply stop attracting after they pass by each other, so the disk has no way to spin past each magnet with more energy than someone was to give it initially. No power can be produced. No violation of the 2nd law.

 

[mathsTKK]

'so the disk has no way to spin past each magnet with more energy than someone was to give it initially'

I don't really get the reason behind actually. Would you mind explain the sentence above? My doubt is why will the disk spin faster and faster if no energy is used to do that? Is magnet the one which provides this energy? Then,if there's a continuous attraction between the permanent magnet on the disk and the magnet near the disk, will the disk spin forever?

Thank you for your explanation :)

 

[Drakkith]

It won't spin faster. The magnets will attract each other equally as they get closer to each other and as they get further away. There is no net acceleration, the disk will simply spin down as it loses energy to friction.

 

[sardar]

Hello, and welcome to PF!

Your question about the magnetic motor and its potential contradiction with the 2nd law of thermodynamics is a common one. The short answer is that yes, the magnetic motor does indeed contradict the 2nd law of thermodynamics.

The 2nd law of thermodynamics states that the total entropy (or disorder) of a closed system always increases over time. This means that energy cannot be created or destroyed, and any energy conversion process will result in some energy being lost as heat, reducing the overall efficiency of the system. In other words, perpetual motion is not possible.

The idea of a magnetic motor may seem appealing, as it appears to create energy out of nothing. However, this is not the case. The magnetic motor relies on the continuous attraction between the magnets, but this attraction is not a free source of energy. It requires an input of energy to keep the magnets in motion, and this energy will eventually be lost as heat, in accordance with the 2nd law of thermodynamics.

The term "free energy" is often used in discussions about perpetual motion machines, but it is misleading. There is no such thing as free energy, as all energy comes from a source and requires an input of energy to be useful. In the case of the magnetic motor, the energy input is necessary to keep the magnets in motion.

In summary, the magnetic motor does contradict the 2nd law of thermodynamics and is not a viable source of perpetual motion. It is important to approach claims of free energy or perpetual motion with skepticism and to understand the scientific principles that govern energy and motion. I hope this helps to clear up your doubts.