Suppose we created a vacuum and spinned a turbine inside it with some amount of force. According to newton's second law it will keep spinning as there is no air resistance, so why can we not make electricity out of it?
20508
There are many videos on youtube in which people arranged magnets in circle and rotated one placing in middle of that circle on a shaft, and the magnet (magnet motor) starts madly and continues its movement. Do they really rotate infinitely? If so, do they from where they get that extra energy to move so fast and infinitely?    EDIT: This question is about real world scenario  UPDATE: I am unable to find that particular video about which i talked about -- I added them to my favourites, but they are all now deleted :( -- there are hundreds of that that kind of videos. Some example videos links
70502
Why was the  refused by Modern Physics? If you please explain me, I just wanted to understand it more.
57289
As an electric motor spins, the energy from the electricity is 'conducted' to the rotor by the magnetic fields.  However, when the motor is stopped, the energy becomes heat and burns up to motor.  What causes this heat to be formed?  Is it purely generated by the current flowing through the wire or is the magnetic field form the permanent magnets involved somehow?  Conversely, why is there less heat when the motor is spinning?  I'm hoping this is not just because the motor contains a fan.
122331
The rotor blades of a lift based wind turbine are shaped like airfoils, so the wind flowing around them creates a lift force which in turn moves them around. From a thermodynamic viewpoint and like answered in  kinetic energy is extracted from the wind during this.  But what goes on from a mechanical perspective? How exactly is the kinetic energy of air particles transferred onto the rotor blades via lift? None of the sites I read gave an elaboration on the how.
68379
I know this might sound stupid and maybe stupid totally, but I need some clarification....  I came through electric motor principle.  and then I came across the following link on DC generators    Now my question is, can't we combine them both to provide DC current with little DC used in motor side? By "combine," I mean using a DC generator coil only at the other side of the coil of the motor in the motor itself. The condition is that the 2 coils are connected via some apparatus that causes the 2nd coil to move along with the 1st coil.   In this way we can use both the mechanical energy produced by the 1st coil and the electrical energy produced by the 2nd coil, right?   This is a great concept if it works, right? Please throw some light on this.
13853
I just saw  demonstration by someone from a Tel Aviv University lab.  What they achieved there is mind blowing. I myself own a levitron that uses the Hall effect to levitate a magnet, the problem with that is the magnet must always be flat facing the Hall effect base, any unbalance will wreck the levitation. But in the case of the video you can see that he isn't constrained by such things, the disk can levitate and stay still at whatever angle and orientation. Instead of being levitated, the disk is simply being held still.   How does this happen? He referred to this as quantum trapping, but I've little idea about what that is....  Also, what material is the base in these demos? Is the circular track in the demonstration magnetic? I assume this is so. Is there any conceivable way for this technology to make objects levitate on any surface?
89713
When a motor, connected to a battery that has a constant voltage, spins without a load it's speed is higher than with load. I'm told that because of back emfs the current is very small when there's no load because of the higher speed. And so when there is a load the back emf is less as the motor spins slower, and so the current is higher.  What is a back emf and what is the relationship between that and the speed of the motor (well the coils inside the motor)?  Is the output energy of the motor constant, whether it has a load or not? (ignoring friction and electrical resistance) because I don't understand how the current can be higher when the motor is (or seems to be) doing more work due to the load?
74183
Why  wouldn't be possible if we are so technological advanced?  It is just a thing that I was wondering for too long. I mean, we are able to create so powerful permanent magnets, like neodymium magnets which can store an massive quantity of energy for a long period of time, but we are not able to use that energy at all. Why?
20558
If air cannot conduct electricity, how can lightning happen?
106035
If I move a magnet towards the coil then the magnet will experience a restive force because of . This way mechanical energy will convert into electrical energy.  But what if the magnet and the coil are a sufficiently large distance apart? The change in the magnetic field travels at the speed of light so the magnet will not feel any restive force instantly. Doesn't this violate the energy conservation law? Because we fix the magnet to a particular point before the restive force arrives at the magnet. And we will able to produce arbitrarily large energy in the coil.  If the magnet starts to move at time t=t1 and lets assume that t0 is the time taken for the flux linking the coil to change due to motion of the magnet.  t0 = (distance between the magnet and the coil/velocity of light)  the magnet will begin to experience resistance at time (t1+2t0). so the delay will be 2t0. In this time period (2t0), magnet is free without experiencing any resisting force. During this time period we can draw current arbitrarily large value by making arbitrarily large numbers of turns of the coil. If energy is conserved, then what mechanism stops us to draw any large amount of power from the coil ?
97759
Our teacher asked us this question during the lecture for Power Electromagnetics. We know that Electric Fields and Magnetic Fields are easily transformable into one another. And they are used greatly in various systems.   He asked us why is it that almost all the electric machines are still based on exchange of magnetic energy? Why isn't electric field used for power exchange and interaction through air gaps for a machine?
17013
My physics instructor told the class, when lecturing about energy, that it can't be created or destroyed.  Why is that?  Is there a theory or scientific evidence that proves his statement true or false?  I apologize for the elementary question, but I sometimes tend to over-think things, and this is one of those times. :)
66257
In , a dry cell battery, a wound copper wire and a few magnets (see image below) are being used to create what can be described as "train". It looks fascinating but how does this experiment work?  Update 8th August 2016: This problem has been completely worked out in a paper that was published in the January 2016 issue of American Journal of Physics.     Link: Am. J. Phys. 84, 21 (2016);
122502
With respect to both gravity and electromagnetism, to the best of my understanding potential energy is added or subtracted from a system based on the distance between two objects such as charged or massive objects.  Would this then imply that when oppositely charged objects or two massive objects are brought together within a small enough radius that the drop in potential energy would be greater than the combined mass of the two objects making the net mass/energy of the system negative?
40049
I would like to know where gravity gets its energy to attract physical bodies?  I know that the law of conservation states that total energy of an isolated system cannot change. So gravity has to be getting its energy from somewhere, or else things like hydropower plants wouldn't be able to turn the power of the falling water into a spinning rotor.  Just to be clear, Lets create an example:  Lets say we have two objects with equal mass close to each other. So gravity does its job and it pulls each other closer, this gets turned into kinetic energy. This is where I'm lost. According to the law of conservation energy can't be created or destroyed and the kinetic energy comes from the gravitational pull so where does the gravitational pull gets its energy.  If that energy isn't being recycled from some where else then that means you have just created energy, therefore breaking the law of conservation.
94475
My question is basically this. Is the second law of thermodynamics a fundamental, basic law of physics, or does it emerge from more fundamental laws?  Let's say I was to write a massive computer simulation of our universe. I model every single sub-atomic particle with all their known behaviours, the fundamental forces of nature as well as (for the sake of this argument) Newtonian mechanics. Now I press the "run" button on my program - will the second law of thermodynamics become "apparent" in this simulation, or would I need to code in special rules for it to work? If I replace Newton's laws with quantum physics, does the answer change in any way?  FWIW, I'm basically a physics pleb. I've never done a course on thermodynamics, and reading about it on the internet confuses me somewhat. So please be gentle and don't assume too much knowledge from my side. :)
47024
I know that potential energy exists for a system of objects. But why? Is there no potential energy for a single object system? I assume that there is.  Consider the earth-object system. Suppose an external force lifts the object above the earth. Then the work done by it gets stored in the earth-object system as potential energy.Right?  Now, my question is that is the potential energy always zero for a single object system.   MY REASONING  If we consider the object only as the system and lift it above the Earth, we are doing positive work on it and filling it with energy and the gravitational field of the Earth is doing negative work on it and draining it of energy. Thus whenever the object is moving it has kinetic energy which is fine. But when it is not moving,i.e. when its weight is equal to the force applied by us, the net work done is zero and so the object should not have any kinetic energy. Does it have potential energy?