Will a can in the ocean float or be crushed?

This week, Phil Sansom has been thinking deeply - or rather, sinking deeply - about this question from listener Richard. "Will a can of soda dropped in the ocean sink until it implodes, or float once it reaches equilibrium?" Here's the answer, with help from the Cambridge Science Centre's Mia Foulkes...

Richard - Will a can of soda dropped in the ocean sink until it implodes, or float once it reaches equilibrium?

Phil - There’s only one way to find out what happens to a can in the ocean - an experiment! I don’t have an ocean, but I do have a really big pot that I can fill up…

...that’s three litres - so if I add six tablespoons of salt, I think that should make seawater…

...now let’s see what happens when I drop in a can of Coke…

...it floats!

Right there on the surface! Richard, the can’s failed your question at the first hurdle - it would have to be denser than the water to sink, before we can learn whether it would implode or hover at a fixed depth. But that’s not the end of it - says Mia Foulkes, from the Cambridge Science Centre...

Mia - This is a really interesting and deceptively complex question, and depends on which country you’re in! In the UK, fizzy drinks contain less sugar and so the can will always have a lower density than water and float. Other countries will add more sugar, and so their cans of soda will sink.

Phil - The difference even extends to diet vs regular drinks - regular Coke will sink, while Diet Coke will float! So let’s take the sugariest of US fizzy drinks as an example, which will have a density of a little over a gram per millilitre.

Mia - Ocean water is at that density at about 5,000 m below the surface. If our can sank to 5,000 m it would sub-surface float because of equal densities. But, it is unlikely the can would get that deep. At 5,000 m, the water pressure would be around 50,000 kPa.

Phil - That’s 500 times the pressure of the normal atmosphere!

Mia - So, if a can of soda sank in the ocean, it would be crushed before it started floating.

Phil - Halc on the forum speculated on how this might happen. The can is a nice symmetric shape, so it will retain that shape for a while, but eventually the top of the can will begin to bulge inward. Given enough pressure, the can might actually dent somewhere allowing the two pressures to equalise and preventing further deformation. It won't ever completely implode - there’s not enough compressible gas.

Mia - Interestingly enough, the average depth of the ocean is 3,700 m. So, in many places, the can couldn’t possibly get deep enough to float, even if it could survive the trip down.

Phil - Thanks very much to Mia Foulkes for that answer. For now, that’s see you later, alligator - because next time we’re answering this question from one of our younger listeners, Johan...

Johan - Why is a crocodile’s skin bumpy and not smooth?