# Forums

## (Sorry) Another Perpetual Motion thread

Though I've been trying my hardest to convince Dad perpetual motion machines don't work, he thinks two electric car batteries with a small wind turbine charging one, while the other one provides motion, then when the battery dies, a relay switch will then power the car via the one that was being charged, making #1 the one being charged while #2 powers the car.

Can someone in very detailed formulas and stuff explain if it will work/why it won't? He won't listen to me :c

DTsea | 5 giugno 2017

No need.

Tbe wind turbine on the towed car will force the towing car to expend more energy than the turbine generates.

lilbean | 5 giugno 2017

Wouldn't a hamster wheel in the frunk be better since it has less drag coefficient?

Remnant | 5 giugno 2017

@Oscarhrodriguez205 (OP, June 5, 2017)

<< Another Perpetual Motion thread ... Can someone in very detailed formulas and stuff explain if it will work/why it won't? He won't listen to me >>

Examples presented as questions might help:

How would you move a ship by blowing air into the sails from the ship itself?

How would you move a car by capturing kinetic energy (from the motion of the car) and feeding it back into the motors as propulsive energy?

How would you move along, if you had to – at the same time – provide energy to a pump feeding that energy back into your muscles?

Are you aware that any capture of energy from the kinetic (motion) energy of a moving car is bound to slow it down, that is, brake it, which is what "regenerative braking" does?

Hence, can you grasp the concept that the kinetic energy capture subtracts from – rather than adds to – the propulsion the car requires to move along?

Rocky_H | 5 giugno 2017

Here are kind of two things:

First off, there is the basic idea that you can not duplicate the same energy. If you are collecting (converting) the energy of the motion of the car into electricity, you are taking it away. It is therefore not present anymore in the motion of the car. (The car has slowed down by the act of your taking away its energy to turn into electricity.)

Now I came up with a great analogy that works pretty well to show how useless this idea is.

Let's say there is a pitcher that is about half full of water. Someone is saying they are going to fill it up. I ask how, and they say, "I'm going to take this cup to pour water into it." Oh, OK. Then I ask where they are going to get the water from. "Oh, I"m going to scoop it out of the pitcher to pour it back in." **stares in disbelief**

The person just thinks that the act of pouring water into the pitcher fills it will add water. This example shows that as long as the pitch itself is the source of that water, you can't gain anything by scooping that water and pouring it back into itself. And the analogy is more complete by pointing out that there are a little bit of losses, where you scoop the water out, but then some drips off your hand onto the counter and is lost. You lose a little bit each time from doing this, so you're worse off than if you weren't even trying to do it. That's the same as in this electric car generating thing, where you're just converting energy back and forth in a circle and losing a little bit both ways in the conversion process.

Bighorn | 5 giugno 2017

Look into Namenda

georgehawley.fl.us | 5 giugno 2017

I think you need 3 batteries.😏

EcLectric | 5 giugno 2017

Nice illustration Rocky_H

Rocky_H | 6 giugno 2017

And I usually see people try to make analogies to other situations that do work, to try to show why this should work too. They appear superficially similar, but the obvious difference is that they have an external energy input.

A gas car uses an alternator to generate electricity while it drives.
** The external input is that it's burning a little bit more gasoline to account for that alternator drag.

A sailboat drags propeller generators through the water to generate electricity for onboard use.
** The external input is the wind. You're just dividing its force between the sails to move the boat and the drag of the generators in the water.

A bicycle has a wheel generator to power a headlight.
** Your pedaling is the external energy input. You just don't notice the tiny bit of extra effort it's taking to spin that generator in addition to moving the bike.

Xerogas | 6 giugno 2017

Add some magnets and his idea should work. You know, to pull the car past all those darn believers in physics!

El Mirio | 6 giugno 2017

Or someone could ask Trump to repeal some of these horrible physics laws, #REAL RED TAPE

Bighorn | 6 giugno 2017