# Tag Info

46

The balls are entering the water well below the surface. The pressure there is much higher than at the surface. The work needed to push the balls into the water at this depth cancels the work gained when they float back up. We can ignore the gravitational force on the balls since gravity pulls down as much as up as you traverse the loop. Mathematically, ...

21

If gas A and gas B are of different density, then the situation sketched is not in equilibrium: the water level on the side of the light gas will be higher. There, the containers are moving down, and you have to push your containers through this net difference in level. You do need to put in energy here, which is probably the piece that you are trying to ...

17

A simple symmetry argument might help here. Try to abstract everything away from your picture that is just a distraction. In the end it might look like this: Why should this move to the left or to the right? It cannot and therefore adding a person and wheels does not change the problem.

12

The energy conservation law is compatible with every single observation we have made inside the Milky Way in science, or outside science, so the empirical evidence in favor of it is overwhelming, diverse, and universal. Theoretically, the case is also clear. Emmy Noether demonstrated that conservation laws are linked to symmetries. The validity of the ...

10

Anything can rotate infinitely, if there is no friction. Rotating an object with constant velocity uses no energy to maintain. With friction it will loose energy and eventually stop. If you add a static magnetic field to the object, it will gain some finite potential energy, which in turn can be converted to kinetic energy. Now if you add a changing ...

9

Thermodynamics does not prevent the trapping of heat. Here are limitations that thermodynamics does impose on the energy balance of the Earth: The Earth's surface can not be (passively) warmed hotter than the temperature of the sun The Earth's surface can not be (passively) cooled colder than the temperature of space Those living on the Earth can not get ...

7

The problem is in the seal. The amount of work to move the seal against the water pressure is the same amount of energy that is gained by the balls when they are pushed up by the water. Even if we remove the seal and we imagine a magic "one-way pass-through" wall, the ball would still need to displace the same volume of water as itself in order to get into ...

7

You do not need to invoke friction. The magnetic forces are in equilibrium by themselves so if you place the magnets in that configuration, they will not spontaneously begin to move. The reason is that there is a corresponding force on the magnets when they are vertical that matches the ones you've already drawn. Let me make a simple model. First of all, ...

6

First of all, nantennas in general don't violate the second law of thermodynamics, so they are not perpetual motion machines of second kind. As long as the total entropy goes up, the second law is obeyed. In other variables, it really means that a part of the incoming heat has to heat the nantenna up but there may still be a lot of energy left for energy ...

6

A (non-accelerated) permanent magnet doesn't produce electromagnetic radiation. It is surrounded by a magnetic field (just like a charge is surrounded by an electric field), but it does not radiate. Especially there's no energy leaving the magnet. Note that for energy flow (as in radiation) you need both an electric and magnetic field, because only then ...

5

Coefficient of friction applicability Saying the frictional force is $kMg$, opposite the direction of motion is a particular physical model. This model is not fundamental, and is certainly not 100% true, although it works pretty well for lots of practical situations. It applies for sliding between two surfaces, and it does not apply for a rolling ball. ...

5

If you need to produce the antimatter from (e.g. electric) energy – e.g. antiprotons may be produced from collisions of proton pairs at the LHC (most of the initial, "invested" energy is the kinetic energy of the protons there) – then you're obviously not getting an economic source of energy because you're converting energy to mass and back which would be ...

5

The second law holds on average for systems of any size, large or small. If you have an isolated contraption containing just a few atoms, and you run it through some procedure (maybe as simple as waiting 5 seconds, or maybe more complicated), there is some probability that the atoms will wind up in a lower-entropy configuration at the end of the procedure ...

5

He's basically saying assume you have some complicated system of weights connect by pulleys, and each weight can be in only one of two states: up or down. But you can trade off which ones are up and down, for example you can make 3 light weights go up by having one heavy one go down, and there are many other moves like this you can do. Now his point is ...

5

In addition to Bernhard's answer, just because three gases (Gas A,B and air - which is itself a mixture of nitrogen, oxygen, and other gases) have different densities, it does not mean they will remain seperated when in a container. In fact, as entropy of the system increases over time, Gas A, B and air will make an even (if heterogeneous) mixture.

5

The speed of any object is constant if there are no forces acting on the object. This applies to light and all other matter. Without forces (e.g. friction), an object that is moving will never stop moving. By "perpetual motion" people usually mean a machine that can produce more work than the work required to run it. It's hard to think of an everyday ...

4

I'm afraid to say that unless we're considering incredibly cold superconductors (which have been known to sustain currents for years), none of these devices work. The first video offers instruction on building all manner of green devices including solar power generators and I'm not sure If it even claims to be a perpetual motion machine. I mention the other ...

4

It doesn't appear to be fraud (as suggested on Skeptics), but rather a good joke. The YouTube video ultimately links to this disclaimer for a great little website. Apologies if I ruined the joke.

4

This is because how much ever force the magnet is applying on the IRON (not any metal) is opposed by an equal force applied by the iron on the magnet! And since the magnet is a part of the vehicle, this force will cancel out the force on iron by the magnet. Magnetic force occurs both ways! Therefore, there is no NET force on the whole vehicle, which is why ...

4

The main point is that Newtonian gravity fields are conservative. What that means is that it is impossible to have a configuration like the one you drew without there being gravitational fields pointing to the left and to the right in the regions where you want to do the 'horizontal' transfer. For example, you might try to achieve this on Earth by taking ...

3

I guess the operative question here (no pun intended) is, what does it mean for a machine to "operate"? If you consider a particle that just sits there and doesn't do anything to be an operating machine, then yes, it is theoretically possible to build one. Just put an atom somewhere isolated and leave it there. In reality, of course, you can't do this ...

3

As others have said, a heat pump with an efficiency greater than unity doesn't have any problem with the laws of thermodynamics. There are still a few problems with this which mean that it isn't as good as it seems. The efficiency of a heat pump depends on the temperature difference - you can get higher efficiencies when you're just increasing the ...

3

Actually, what is impossible is a perpetuum mobile which is a machine or system that breaks the first or second law of thermodynamics. Planetary motions break none of those laws, therefore there is no contradiction with their "perpetual motion". The question of the end of Earth's orbit is a different one though. Certainly, the Earth's orbit will end, most ...

3

There is no reason why you couldn't build a motor using superconducting magnets, or build a simpler homopolar motor using a length of superconducting wire. There would be no heat dissipated due to electrical resistance, but of course there would still be mechanical resistance due to friction on the moving parts. The energy needed to overcome this, and to ...

3

Now I'm wondering if a perpetual motion machine of the second kind (a machine gaining energy by cooling down the environment) would be possible in nanotechnology. As a result such microchips would lower the entropy of the universe. A thousand times no. If a concept lowers the entropy of the universe in a non-superficial sense it is always false. As ...

3

It does not work for the following reason. Let's look at the right side, where the containers float to the top. When a new container enters at the bottom (from water to gas B), it pushes some gas B away, so it can occupy the space. The pushed away gas B has nowhere to go, but up. Gaining height means potential energy. That is energy used, to make the ...

2

Zassounotsukushi's answer is good, but I want to emphasize that there is a mistake here: when I apply a force very very small in magnitude as compared to KMg, then an equal amount of frictional force will be exerted by the surface on the sphere at the point of contact. The surface does not exert an equal force. The way friction works is that it ...

2

2012-03-08.17:37 EST: Kian Mayne: Good question! Since everyone knows energy is conserved, the title of the Gizmodo article summary sounds instantly self-contradictory. It certainly makes you want to figure out what the authors really meant, since unless they completely misunderstood the original paper, they clearly did not mean that you get 2.3 times as ...

2

The left magnet is pulled forward, pulling the car behind it. The right magnet is pulled backward, pushing the car ahead of it via the rod that attaches it to the car. (The fact that the rod loops over the car and attaches to the back makes no difference.) If the rod is flexible, the car will move forward as the magnets move closer together, but only ...

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