Why is an unopened carton so much harder to shake?

28 November 2010

Question

Hi Chris and Team,

Love the show.

I have a physics question. I don't think it's been covered much or at all, even though it's of course, incredibly important! I can't find much info online, mostly because it's difficult to phrase the question in a search engine. Here goes...

INCREDIBLY IMPORTANT PHYSICS QUESTION
When I shake a new carton of orange juice (the good stuff, no concentrate for me), it is difficult to shake until I break the seal. What's up with that?

The new carton is under a vacuum (well, a tiny vacuum, I know it's hard to get a "good" or "real" vacuum even in outer space...), so I would think there's a good few centimetres for the juice to slosh around free and easy. But when you crack the seal and let air fill the void, you've got this dense gas, so it should be harder to shake now...but it's much easier!

This could be all perception, but others have observed this effect.

What is going on?

Cheers,

Wink

Answer

We took this on as this week's Kitchen Science!

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