The self resetting pendulums are described in the picture below. Yes, I'm aware of the laws of thermodynamics so no need to post snarky links to physics websites. This is a thought experiment or a mental exercise about a simple idea that came to me in a dream.

Self Resetting Pendulums


closed as off-topic by Aify, Jorge Aldo, sdrawkcabdear, Vincent, HDE 226868 May 12 '16 at 1:40

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – Aify, Vincent, HDE 226868
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ You're going to need to add a lot more explanation, because right now it looks like you do need a refresher on basic physics. $\endgroup$ – pluckedkiwi May 11 '16 at 20:50
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    $\begingroup$ What, exactly, are you asking? You might as well ask, “In a universe where the laws of thermodynamics and conservation of energy do not hold, can I produce limitless energy from the metabolism of a cat and a magic energy amplifier?” I believe that you need to address the aerodynamics of winged pigs. $\endgroup$ – Peregrine Rook May 11 '16 at 21:13
  • $\begingroup$ Snarky comment - well done $\endgroup$ – user2708841 May 11 '16 at 21:55
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    $\begingroup$ I'm voting to close this question as off-topic because it is about a concept of physics that might be better explained on the physics comunity. $\endgroup$ – Jorge Aldo May 11 '16 at 22:36
  • $\begingroup$ The question in itself is not bad enough to be downvoted in my opinion (just closed/moved to physic, ignorance is not a sin and don't tell me that you were all born with a PHD in thermodynamic) however the fact that the op is not asking a question but asking for a confirmation of something he already think is true makes it totally useless for him (he will not get what he is looking for) and everyone else. (btw: the answer is no because 2nd law of thermodynamic, not what you are looking for) $\endgroup$ – Nyashes May 12 '16 at 1:35

This IS a perpetual motion machine.

From the laws of physics the pendulum can only reach THE SAME height as the one from where it was launched and then only if does not lose ANY energy while they travel. The aerodynamic drag is enough to make the height the pendulum reaches on the first trip lower than the height from which it was launched, and the height reached on the return trip even less high, and so on. Add to it any form of energy draw from it and it will never reach the other side to launch any other pendulum. At long term it will stop.

No matter how you look at it. The pendulum has a constant amount of energy equals to the potential energy that is stored into it at the launch height. It becomes kinetic energy while it travels down, and then becomes gravitational potential energy again while it climbs. Provided that there is no energy transfer from the pendulum to any other thing, it will beat forever.

As soon as you transfer energy from the pendulum, the amount of energy in the system is decreased. Energy is finite, so its motion will eventually die down. On earth this energy drain is usually caused by aerodynamic drag (For a pendulum).

If, lets say, your pendulum is magnetic and it successively makes its magnetic fields cross a series of coils while travelling up and down, it will cause a electric voltage to develop on such coils. But, as soon as you start drawing current from the coils, effectively draining energy from it, the coils will produce a force against the movement of the pendulum, effectively draining its kinetic energy and making it move slower at each pass.

By the way, locking the pendulum after the first trip solves nothing. The locking mechanism itself needs energy and this energy will be drained from the pendulum, if you drain energy from the pendulum while it travels from one side to the other and expect it to move a locking mechanism at the opposite side, you have two energy drains. If the locking mechanism is at the same height as the pendulum when it was launched, it will not have enough energy to move the locking mechanism when it reaches the other side. So, this system wont work.

  • $\begingroup$ "and the height reached on the return trip even less high" There is no return trip. The pendulum gets reset by the gate lock. $\endgroup$ – user2708841 May 11 '16 at 21:52
  • $\begingroup$ "the pendulum can only reach THE SAME height" That's ok and is to be expected. There is a bar sticking out on each pendulum that negates any friction loss and sticks into the fence lock, resetting the pendulum. We just want to capture some energy from it's movement on 1 single swing. $\endgroup$ – user2708841 May 11 '16 at 22:02
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    $\begingroup$ there is no such thing as "negates any friction loss" $\endgroup$ – Jorge Aldo May 11 '16 at 22:27
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    $\begingroup$ but it does not null it. when you say "any" air friction, you imply no friction at all. $\endgroup$ – Jorge Aldo May 11 '16 at 22:35
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    $\begingroup$ if you take an infinitesimal ammount of energy from the pendulum, it will rech an infinitesimaly smaller height on the first pass, an infinitesimaly smaller height on the return and so on. what you imply is that if you take an infinitesimaly small amount of energy from the pendulum it will return to the same height as if no energy was lost at all. thats not true. $\endgroup$ – Jorge Aldo May 11 '16 at 23:03


How are you extracting energy from this system? If you are getting it from the pendulum, then the pendulum will slow down and won't reach the same height at the end of the swing as it did at the beginning. This lower starting height will reduce the height at the end of swing 2 and so forth until the pendulum is at the bottom. So you can't both extract energy from it and have it go forever.

What if you just let the pendulum go and didn't extract energy? Well air friction will gradually slow the pendulum and stop it.

There real problem in the question is the word "limitless" You can definitely get energy out of a pendulum set up, but not limitless. Limitless energy would be enough energy to launch the earth out of orbit and create a new galaxy or an infinite number of galaxies.

Energy generation is a misnomer, we never make energy we just convert it between various forms chemical kinetic potential electrical.

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    $\begingroup$ "How are you extracting energy from this system?" Energy is extracted just from the swinging motion of the pendulum. $\endgroup$ – user2708841 May 11 '16 at 21:55
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    $\begingroup$ @user2708841 How?? does the pendulum push something or hit something, does its gravity pull something? $\endgroup$ – sdrawkcabdear May 11 '16 at 21:56
  • $\begingroup$ The swinging motion turns the wheel as shown in the picture. It's a simple yet clever idea. $\endgroup$ – user2708841 May 11 '16 at 21:59
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    $\begingroup$ This would still take kinetic energy from the pendulum to spin the wheel and eventually cause it to stop. You are welcome to try it yourself, I'd be glad if you invented a perpetual energy machine. $\endgroup$ – sdrawkcabdear May 11 '16 at 22:07
  • $\begingroup$ why do you say "eventually" - they don't swing back and forth like you are imaging. They are RESET each swing. $\endgroup$ – user2708841 May 11 '16 at 22:08

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