The speed of sound in water is much faster than in air. It does depend a little on your water - fresh vs salt, cold vs warm, pressure - but it is much faster in all conditions - in the neighborhood of 3200 mph or 1400m/s. We can hardly push things through air (at sea level) at those speeds. The fastest bullets reportedly have an initial velocity about 1500m/s. Theoretically, there would be a similar compression of the sound pressure waves as you approach the speed of sound wave propagation in water, but I can not at the moment imagine a real-life situation where this would be meaningful.

First Q-- A mile a second. Second Q-- Yes, but who knew it? Was what we saw one of those? The speed of sound in water is over four times the speed of sound in air. Roundly about 1500 meters/sec. (5,000 fps almost 1 mile/sec.) That is well over 5440kph (3350 mph)-- a velocity realized in the atmosphere by projectiles,rockets, the X-15 and meteors. But in water? I found this news remarkably to the point: "July 18, 2005. The Dec. 26 Sumatra-Andaman megaquake did more in the Indian Ocean than make tsunamis. It made a lot of undersea noise. Five hydro-acoustic sensor stations... show the rupture... Propagating... for 400 miles at 5,760 miles per hour, then (for the last 100 miles) slowing to 3,350 miles per hour...." http://dsc.discovery.com/news/briefs/20050718/megaquake.html Accordingly, may we observe over 4 minutes undersea water-supersonic event (movement of the place of rupture,) which slows to the speed of sound in water for nearly two minutes longer. May we not suppose the tsunamis to be resultant, water-supersonic "booming?" Remember, the "boom" itself isn't supersonic. Also, the shock wave doesn't result from "sound" but the limits of compressibility of the air. From the object forcing to displace the air. At mach 1, the gaseous composition of the atmosphere is compressed to the threshhold of liquifaction, hence incompressibility. Instead of being displaced, the air squirts out all around. You can find pictures of water vapor recondensing resultant from this change of state at transonic zones in jet place flight. Try "Vapor cone" http://www.wilk4.com/misc/soundbreak.htm Water doesn't compress, but does have a "compressibility" function that works out the way energy is stored, distributed and discharged in water's liquid state-- its "modus of elasticity" is different in water from any other materials. Booms are extreme energy forcing the air. Tsumani's do the sea.

a meniful use wold be a torpedo that woldn't be picked by sonar

A sonic boom is produced when the particle in a medium is travelling at a speed faster than the speed of sound in that medium. The ratio of speed of a particle to the speed of sound is defined as mach number, M. M = velocity/c ; c-> speed of sound. Not the speed of sound in air is 300m/s (approx) so a missile traveling at 450 m/s (M=1.5) certainly will have a sonic boom (Mach wave) assoicated with it. On the other hand if a torpedo (underwater) was traveling at the same speed(450m/s) in water it wouldn't cause a sonic boom becuase the mach number M = (450)/1500 approx 0.33 < 1. This is one reason why an aircraft might be able to achieve higher speeds at lower heights without sonic boom(M>1) than at higher altitudes where the speed of sound (so is the density of air) is much lower. Higher the density greater is the speed of sound. So speed of sound in solids is way higher and we cannot possibly create a sonic boom ( M > 1) in solids ( atleast with the existing technology). Some food for thought : When electricity is flowing in a wire what is its speed. Isn't there a similar ratio or limitation ? We know that this cannot be comapred to the mechanicl waves in previous argument. But how about the electrons which travel in the wire. Prasad, CFD Engineer, NM

How much power (horsepower?) does a US Trident II (Ohio-class Tennessee-forward) "boomer" missile submarine use to go at top (revealed) speed (23 kt/25 mph)? 18,750 tons/560 ft Now, how much power would it take for this submarine need to go at the speed of sound (3400 mph)? (Assume that the sub's hull would withstand the stress of being forced through water at such a speed.) A rough estimate of the power required of the SG-8 based power plant to go at 3400 mph is (3400/25)³ = 2,515,456 x as much power. If the SG-8 plant's power is, for example, 100,000 HP (used for propulsion), the power required to go at the speed of sound in water would be somewhere like 250,000,000,000 HP.

Though the speed of sound is around 3200 m/h under water (around 770 m/h at sea lvl) making an object go greater than 3200 m/h underwater would not create a sonic boom, not to mention be neer impossible. A sonig boom hapens because air gets compressed into a "wave" of moving particles causing a loud sound. Water, has such a low compressability that ths would be undetectable. Not to mention that water is so much more dense than air there would be the problem of the object exploding under millions of pounds of pressure.