# Can the sound barrier be broken underwater?

Is it technicaly possible to build a submarine or a torpedo which could go faster than sound in water?

Slightly different take inspired by the wording of the OP’s title: I am wondering whether a natural object can break the sound barrier underwater? Examples might be meteorites falling into the ocean, or rocks blown apart by underwater volcanic activity.

Only with a huge amount of power behind it. Water has very low compressibility, and making it get out of the way before a pressure wave reaches it would be highly energy-intensive.

But you can make a torpedo go darned fast. The Russian “Shkvall” moves at 100 meters per second or so. It makes a huge racket, but the idea that it can get to the target too fast to be counteracted.

According to this site, the speed of sound in sea water (assuming 3.5% salinity) at 20C is 1522 m/s. For the metrically challenged, that’s a tad more than 3400 mph. I rather doubt that any man-made object would be able to achieve that speed underwater using today’s technology.

Water isn’t very compressible but it is to some extent. The bulk modulus of water is 2.2 *10[sup]9[/sup] N/m[sup]2[/sup] which is about 1/50 that of steel. So I suppose there would be a shock wave at supersonic speeds in water?

There are shock waves at subsonic speeds too but at supersonic speeds you get the nice distinct cone shaped one.

I’m sure a supersonic shockwave could be created but dont expect to do it with stuff in your garage. 1,500m/s is greater velocity than any conventional gun I’m aware of but perhaps a lightweight sabot could get a sub caliber projectile going that fast. it wouldn’t stay supersonic long but enough to document a shock wave.

Well, if you used a nuclear bomb for propulsion, getting that sort of speed underwater should be very possible.

Granted. Could you sustain that kind of speed, though? Hmmm, an Orion-powered submarine!

Could you give a description of just how? An explosion shockwave travels, by definition, at the speed of sound and nuke-u-lar bombs are not exempt from this AFAIK.

No, a sound wave travels at sound speed. A shock wave is by definition faster than sound. It’s basically molecules moving faster than sound speed and bumping into others, causing them to do the same in turn.

But then you wouldn’t really be traveling through water anymore, more of a vapor I would guess.

That’s an interesting point. For any accelerating body in water (assume virtualy unlimited energy), wouldn’t there be a point at which friction against the water would heat the water up enough to basically create something of a “steam leayer” in advance of the moving object?

How about if lieu farts in his bathtub? That should be all the proof anyone needs, provided a video records this event.

::d&r::

Actually, there are projectiles that move faster than the speed of sound. The technical difficulty is to seperate the projectile from the water using cavitation to create a bubble There was an article on the American version in Scientific America a few years ago. Google RAMICS for more info.

Hmm, yeah. I guess the noise coming from a Piper Cub is a “shock wave.” It is a pressure wave that travels at the speed of sound in the medium.

Shock waves are discontinuities in pressure, density and other properties. In a real fluid, the discontinuity gets smeared out somewhat by viscous effects so they’re not a real discontinuity, but they’re considerably sharper than subsonic pressure waves. If you extend your definition of “shock” to mean any pressure wave, you’ve made the term meaningless.

High speed underwater projectiles usually use a ‘gas’ (usually exhaust) to create a bubble of ‘air’ which the thing goes through, or is able to ‘push’ water away from the projectile fast enought that the object is traveling through a vacuum (only the tip travels throught the water).

Germans seem to have that beat.

Read up on “Supercavitation”…lots of research being done in this field.

Here is a possibility. According to Wikipedia, using a railgun, “20 kilometers per second has been achieved with small projectiles explosively injected into the railgun.” So maybe it could be done if you pointed a railgun at the water.