Dolphin Cavitation. They swim until it hurts but no Sonoluminescence.
Cavitation is normally associated with boat propellers. When the tips of the blades move fast enough through the water, and sufficient pressure changes happen at the tip, then it can force a small bubble of gas to form.
The bubbles form, then implode. The implosion causes stress on the metal and over time will cause pitted wear.
Cavitation is not exclusive to man made impellers, propellers and valves. It also happens in the marine animal kingdom. In particular, the pistol shrimp and mantis shrimp create a stunning shock wave because of cavitation. By 'stunning', we mean it stuns or kills small prey.
Dolphins are very fast swimmers. Near the surface, a dolphin such as an orca (killer whale) can reach 54 km/h but they cannot go faster. They have the muscle-power to go faster, but it hurts too much. When a dolphin beats its tail, this creates a big pressure change and when fast enough, tiny cavitation bubbles form and implode. You can imagine that this would hurt, and it does. It is this pain which limits the dolphin's speed.
Tuna can exceed this threashold because they have no nerves in their bony tail but they pay a price of damage to the tail.
At depth, pressure increases, and so the cavitation effect happens only at higher speeds. Therefore, dolphins probably go much faster than at the surface. This would account for the observation that the larger dolphins have ample muscle power which is not the limiting speed factor at the surface.
Sonoluminescence and Dolphins. (Not!)
A more controversial topic is sonoluminescence. This is where ultrasound can be used to stimulate a bubble in water and produce a very short pulse of light. The duration is 35 to 380 picoseconds.
According to a well written, but dubious looking reference : HERE, The temperature inside one of these ultrasonic stimulated bubbles can reach 1,000,000 K and it's natural to compare that to the surface of the sun at about 5,800 K. The pressure in the bubble on collapse is something like 100,000,000 times atmospheric pressure reaching more than Mach 4 and over 100,000,000,000 g. This is a concentration of acoustic energy by about a trillion times. It is probably these impressive numbers which link (in my opinion faulty) speculation between sonoluminescence and fusion experiments or pseudo-scientific free-energy devices.
Dolphins use ultrasonic emission. This is well known, and there are some claims that this ultrasound is used to create sonoluminescence. Although a dolphin can create several hundred clicks per second at a pulse frequency of up to 150 KHz, this is too short to set up cavitation. [ Ref: Fundamentals and Applications of Ultrasonic waves - J. David N. Cheeke , 2002, CRC Press, ISBN: 0-8493-0130-0 ] The video above states that it takes about 4 microseconds for a bubble to collapse and produce light.
So if you read that dolphins deliberately or even accidentally create sonoluminescence via sonic pulses, then be sceptical.
- Dolphins swim so fast it hurts - life - 28 March 2008 - New Scientist
Powerful marine swimmers have physical limits on their speed over and above outright strength, and bony tailed tuna have an advantage
- Research Uncovers Possible New Explanation For Sonoluminescence
An Ohio State University physicist may have uncovered the atomic process behind sonoluminescence, an effect in which ultrasonic waves break against the surface of a water bubble and heat the atoms inside until they glow.
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