If you had a torpedo (or whatever) that could go faster than speed of sound in water what would happen at the point the torpedo exceeded the speed of sound in water? Aqua sonic boom of some kind, or nothing… or what?
According to this site the speed of sound in water is 1480 m/s or 4856 ft/s or more than 3000 miles per hour.
Of course there would be a sonic boom, it’s exactly the same principle. When it reaches the speed of sound, all it’ssound waves essientally bunch up together as the sound producer is travelling at the same speed as them and via constructive interference make one big sound wave.
But water is a LOT less compressible than air. I’m thinking that would make a big difference in the ability to even approach the speed of sound underwater.
Things do move faster than sound in water all the time, but it doesn’t produce a “boom”. Desmostylus’s quote almost mentions the right term: “cavitation”. A “hole” opens in the water that will collapse back on itself once the fast moving object goes on.
The tips of propeller blades do this if turned fast enough. This is not good: the cavitation can damage the blades, engine efficiency is lost, and (most imp. for navy purposes) the noise of the collapsing bubbles is easily picked up on sonar.
For awhile rumors were flying that a (malfunctioning) prototype supercavitating torpedo is what sank the Russian sub Kursk. I believe it was generally discounted later.
That just isn’t right. Cavitation is “cold boiling” of the water. The pressure on the forward side of the propellor becomes so low that the water boils.
Cavitation can also cause dam spillways to corrode in much the same way as they might a propeller, causing catastrophic failures in very short amounts of time.