A true perpetual motion machine doesn't just keep spinning forever:

if you were to set an object spinning out in intergalactic space,

in some ideal true vacuum, it would keep spinning forever.

You just wouldn't be able to get any useful work out of it.

If someone actually built a perpetual motion machine, a true one,

it would give out more energy than is put in:

enough to overcome friction, enough to overcome air resistance,

enough to keep going until mechanical failure.

And like a wind turbine,

it'd let you take some of that extra energy for your own use.

There are, obviously, some physics objections to this.

The laws of thermodynamics always hold true.

This here is a device made by Thomas Young in 1807.

It is the original, two centuries old

from the archives of the Royal Institution in London,

which is why I have to wear gloves to touch it.

It's an unbalanced wheel,

and there have been many perpetual motion machines like it.

There was a giant one in Los Angeles in the early 20th century,

advertising a café: and according to Popular Mechanics,

it kept going until there was a city-wide power cut.

And there was an inventor in 1829 who was sure

that a carriage with conical wheels

would roll around the world “'till time shall be no more”.

They all work on the same principle:

cheat the centre of gravity so it's always on one side,

constantly unbalanced in the same direction.

In this case, if you draw a line down the middle,

there are more ball bearings on one side,

so that side should be heavier,

and when one gets near the top...

...it rolls over, so that side over there is constantly being pushed down.

This doesn't work, obviously.

And that's why Thomas Young built this machine:

to demonstrate that it's impossible.

There may be more ball bearings on that side,

but the ones on this side are further away from the centre.

No matter how much you complicate it,

this wheel will just rock back and forth

and eventually settle where the centre of gravity is lowest,

or where friction stops it.

But imagine if perpetual motion machines did work.

Which isn't difficult to imagine, apparently:

there are all sorts of snake-oil companies

who successfully sucker investors into giving up surprising amounts of money,

and then never produce any actual proof of a working prototype.

There have been so many attempts that both the US patent office and the UK "pay-tent" office

refuse to even entertain the idea of perpetual motion machines.

Now, you can argue physics and thermodynamics all you want,

but there's a more common-sense argument against perpetual motion machines,

against the idea of free energy.

Because regardless of how it's powered,

whether it's an unbalanced wheel or something else,

if you have a magic box that can give out more energy than it takes in:

what happens if you use a small one to power a bigger one,

and so on, and so on, and so on?

You could start with something the size of a grain of sand,

and rotate the Earth with it.

Or what happens if you plug it into itself?

If you have something that multiplies the energy you put in...

then after a few seconds, you've got a bomb.

Thank you very much to the Royal Institution!

Over on their channel I'm debunking three other types of perpetual motion machines

along with someone from their team.

Go check it out!