# Perpetual Motion Machine

## Main Question or Discussion Point

I just read about a new perpetual motion machine and it looks like it will work. You take a cat and tie a piece of toast on to its back. then you butter the toast and toss the cat into the air. Since the toast has to land butter side down and the cat always lands on its feet it spins forever.

Related General Discussion News on Phys.org
lisab
Staff Emeritus
Gold Member
I don't think it would spin forever, because eventually the cat will die () and dead cats don't have to land on their feet.

When the cat hits the ground the toast hasn't really landed. Thus once again confirming that the laws of physics do hold!

BobG
Homework Helper
That theory about toast always landing butter side down is just a myth. The chances of landing butter side down depend on the ratio between table height and toast length.

For a standard 5" piece of toast, the chances of landing butter side down is only better than 50% if the table is between 12 inches high and 110 inches high (approximately). The chances are better than 90% between 30 inches high and 70 inches high.

If you use a larger piece of toast, say a 12" piece of toast, the chances of landing butter side down are better than 50% when the table height is between 30 inches high and, uh, really high. The chances of landing butter side down are better than 90% when the table height is between 75 inches high and 170 inches high.

And, naturally, that assumes a perfect landing surface that will absorb virtually all of the bounce. The worse the landing surface, the more likely you are to get a lucky bounce and have the bread land butter side up.

Would it help if the cat was tossed onto a trampoline??

dst
When the cat hits the ground the toast hasn't really landed. Thus once again confirming that the laws of physics do hold!
Well at least the laws of statistics are broken, given that the cat always hits the ground instead of butter. I think we have an infinite improbability drive here, not a perpetual motion machine.

BobG
Homework Helper
The link in that article details experimentation on toast droppings: http://cockeyed.com/science/toast/toast1.html. They're bad at math (2/20 is a 10% survival rate, not a 5% survival rate), but that might just be a side effect of sticking a knife in the toaster to free a stuck piece of toast. I don't think Brooke paid enough attention to making the sure the plate was always at the same angle, either. A better test would have been to slowly push the toast towards the edge of the table until its center of gravity was just beyond the table edge. I think that would have gotten more consistent results.

All in all, I'm not even sure they're scientists.

Last edited by a moderator:
I've never dropped a piece of toast off of a table. I don't even know how that's possible. I've only dropped it out of my hand either because it is too hot, in which case I haven't buttered it yet, or when I was in the process of buttering it.

BobG
Homework Helper
I've never dropped a piece of toast off of a table. I don't even know how that's possible. I've only dropped it out of my hand either because it is too hot, in which case I haven't buttered it yet, or when I was in the process of buttering it.
Personally, I avoid those problems by buttering and spreading jam on the bread before inserting it into the toaster. It's a good toaster, too, except the side with the butter and jam tends to stick to the ceiling.

wolram
Gold Member
There must be an exception to the rule here, if one is holding the toast and it breaks i sure 9 times out 10 it will fall butter side down.

Moonbear
Staff Emeritus