Is this a proper perpetuum mobile?

today I want to investigate one particular perpetuum mobile machine. First when I wanted to write this post I wanted to let it open ended since I did not know the solution for why it does not work but I have found it so here you go:

Physics is basically based on the fact that energy and mass are conserved. If you were able to put enough strong evidence against it, modern physics would basically collapse, this is the foundation.

Now perpetuum mobile is a machine that is trying to break this law, but not very succesfully since none was ever built. Perpetuum mobile is a machine that gives out more energy than it needs for running.

Performance is larger than power and effciency is larger than 100%. This is not possible though you can check your basic physics skills by debunking these machines.

One of the most common “perpetuum mobiles“. As it turns it is supposed to create torgue and rotate forever.

It has been while since I saw what is called “Brownian ratchet” and I was simply stucked. It is kind of different from other “perpetuum mobiles” since it uses what is called brownian motion to work.

Feynmann was one of the guys who popularised this machine and also showed it flaw.

In the box 1 you have small paddle wheel. Particles bump into it because of brownian motion, that is a motion of small particles that goes indifinetely (this is type of thermal fluctuation).

This paddle wheel can only turn in one direction because in the other box you have ratchet as you can see above. The paddle wheel turns one way lifting up something or simply doing work. Where is the problem?

I remember asking my teacher about this. She said that it would really be perpetuum mobile. I knew she is not a good one. Now I did not know but I was sure that there is some flaw in this and I found that there is but I did not find explanation.

Today I found wiki page about this “Brownian ratchet” and they basically say that if the pawl is the same temperature as the paddle it will also undergo the same brownian motion sometimes jumping up and down. The thing is that we can not forget that the thing is also extremely small. If it would be different temperature it would work but based on thermal difference which over time disappears.


Explaining equations easy way

today I want to talk about simple physical equations and how you can check if they are right or not.

Lets start with the equation of distance in the most simple way.  How do you find this formula anyway? Well we want to know how distance traveled is calculated.


Now on the right side there should be something that corresponds to distance. There has to be time because we are talking about traveling in some time.


Distance also depends on how fast you are traveling, which means velocity has to be there. Now if both time and velocity are bigger you will get also bigger distance so there will be multiplication between them.


From this we can conclude that:

v=s/t     this makes sense because velocity will be big when you travel for short time great distance.

t=s/v     this too makes sense because time will be great when you will go slowly great distance.

This is all intuitive, you do not remember any equations because those you can always get just from pure logic.

I can follow with the equation of inertia:


Inertia describes basicly how hard it is to stop something. Just from personal experience, when is it hard to stop something? When it is heavy and when it is fast.


What units will inertia have? Well you can always compare only same units so the units that come up from “m*v” must be the units of inertia.

p=m*s/t (now here we have the basic units)


The unit of inertia is kilogram on meter per second!

Those equations that have only two parts can be made really fast this way if you do not remember it exactly.

There is this important part with the same units. When you do some problem in physics you usually first just take all the letters and try to combine them until you get the final “sentence” and then you enter all your values. This is very effective and it is good to check you final equation, look at this for example:


Here it would be hard to imagine if it makes sense like we did with the formula for distance but we can get insert all the units and check if the right side is the unit for P – performance. (here m is mass, g is gravitational acceleration, s is distance, t is time). We know that the unit of performance is watt and watt is: kg*meter^2/second^3

So now for the equation we insert the values:



Now we know that we are right even though we maybe started with P=W/t (W is work) and we were not sure if the conversion was right. The units correspond to what we know about performance.