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How to Tell if an Egg is Raw


I’m going to show you how to tell the difference between a raw egg and a boiled egg without breaking the shell.  So, in this egg box here I’ve got four eggs and two of them have been boiled and two of them are raw.

So here’s what you want to do if you want to tell the difference.

You take an egg and put it on a flat surface and spin it.  Then you put your finger on it very quickly to stop it.  And I can tell that this one is cooked so let’s put the raw ones down there.  So I’m gonna put the cooked ones on this side and the raw ones on that side.

So here’s the next one. Spin it, put your finger on it to stop it.  Oh, it kept going, that one, so I think that one is raw.

Next one – get it going, put a finger on it – and that kept going so that one is raw.


This one stopped and that one is cooked.

Now what’s going on here is that the difference between a raw egg and a boiled egg is that the boiled eggs, the cooked ones, are solid on the inside and the uncooked ones are liquid and that’s really important.  What’s going on here is something called conservation of angular momentum.  So when I take a cooked egg, when I start it rotating and giving it angular momentum it’s just gonna keep going, it’s gonna keep going because that’s what happens; as long as it’s got angular momentum it’ll keep spinning if there’s no reason to stop.

So I get it spinning and I put my finger on it – put my finger on it very briefly – and I stop the whole egg all in one go; I’ve taken away its angular momentum and the egg stops spinning. That’s a cooked egg.

When I take a raw egg and get it spinning…so I’m giving it angular momentum, all the egg’s got angular momentum, put my finger on it, I take my finger away.  Now when I put my finger on it I only stop the shell but I didn’t stop all the liquid inside ‘cause it’s not connecting and the liquid inside still has angular momentum.  So when I spin it and I stop it, I stop the shell, the liquid inside is still spinning so the egg keeps spinning.  And that is a demonstration of angular momentum, it’s very useful.  And angular momentum like this, the fact that if you spin something it keeps going, is really useful for keeping satellites stable, for example; it’s the reason we have great big rotating storms on the earth, it does all these things and you can demonstrate that with eggs. 

And just to prove I got it right, I’ve got a bowl and I’m gonna look stupid if this goes wrong.  So I think that this one is a raw egg [cracks it] and it is.  And I think that this one is a cooked egg [cracks it] and there we go, cooked egg, solid egg. 

So angular momentum is great because it explains both eggs and how to keep satellites stable.