What happens when a bomb explodes underwater?

08 March 2009

Question

What happens when a bomb explodes underwater?

Answer

Dave - Well when any bomb explodes the first thing you're going to get is a lot of high-pressure gas because you've taken a load of solid and turned it into gas. It wants to expand. Water isn't going to move away nearly as quickly as air does. The pressure's going to remain very high, pushing water away. The fastest the water can move away is roughly the speed of sound in water. That's 1400m/s. You're going to form a bubble. As that water is pushed away very fast you're going to get a second powerful sound wave or pressure wave moving away from it. If the water doesn't compress that's going to have a very high pressure and do a lot of damage which is why depth charges can destroy strong things like submarines, even 10-20m away. Apparently it's way that there's a theory of how you might be able to blow up safes. If you fill a safe with water an drop a small charge in then because the pressure change is so much greater it might blow the door off.

Chris - That's because all the pressure is being exerted on the safe. If you were to just stack a load or dynamite at the front of the safe, some of it would hit the safe but a lot of that pressure would go out.

Dave - The gas that's produced, all that extra volume that's produced is pushed on the side of the safe. Normally you can just compress the air inside the room. Kat - It would be more explosive if you fart in the bath as well.

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