I know that when an object exceeds the speed of sound ($340$ m/s) a sonic boom is produced.
Light which travels at $300,000,000$ m/s, much more than the speed of sound but doesn't produce a sonic boom, right?
Why?
[Physics] Why doesn’t light, which travels faster than sound, produce a sonic boom
acousticselectromagnetismspeed-of-light
Related Solutions
Have a look at http://en.wikipedia.org/wiki/Speed_of_sound#Basic_formula for info on how the speed of sound depends on the medium it's passing through.
Generally the important factors are the stiffness of the medium and it's density. To get sound to travel faster you need a stiffer lighter medium. For ordinary matter you'll never get speeds at anything like the speed of light because the electromagnetic forces that hold matter together are far too weak to permit this. However in neutron stars the stiffness of the degenerate matter they're made from is determined by nuclear forces and the speed of sound can approach the speed of light.
Sonic boom refers to the explosive sound caused by the shock wave from an object traveling faster than the velocity of sound. Yes, It's actually spoken out as breaking the sound barrier.
Felix jumped from an altitude of 39,044 km (which is 128,097 ft.) and reached a peak speed of 833 mph. Yes, He did produce the Sonic boom. Most likely, we use the term Breaking the sound barrier while considering air-crafts like "Concorde" because they could be easily sensed. But in case of Felix, he produced
"It was Mach 1.24. Our ground recovery teams on four different locations heard the sonic boom," said Clark, a former high-altitude military parachutist and NASA doctor who worked on escape systems for space shuttle astronauts.
That "Mach 1.24" reading is comparable to the shock waves produced by Space shuttles...
But how does this number change as air density decreases?
Velocity variation of Sound: Indeed, Sound varies with Temperature and also with Density. Also, the state of matter (which refers again to density). It travels faster in liquids and even more faster in solids (like 5120 m/s in Iron)
In general, the speed of sound in a gas is given by Laplace correction of Newton's formula. For solids, see Wiki ('cause it's not necessary now...) $$v=\sqrt{\frac{\gamma P}{\rho}}$$
Applying Ideal gas law and using density of air ($\rho=1.293$ $kgm^{-3}$), we could find that the velocity of sound increases by 0.61 per degree celsius rise in temperature in air. Also, the velocity of sound in a gas is inversely proportional to the square root of its density. But, it's independent on Pressure (Don't believe in appearance of the formula). This is because increase in pressure, also increases the density of gas. This could be achieved by using different gas densities (at same volume & pressure).
Also, See the Atmospheric variation of sound's velocity.
Best Answer
A sonic boom is produced when a macroscopic object (say, roughly: larger than the average spacing between air molecules, $\approx 3\,\mathrm{nm}$) moves so fast that the air has no time to “get out of its way” in the usual way (linearly responding1 to a pressure buildup, which creates a normal sound wave that disperses rather quickly, more or less uniform in all directions). Instead, the air has to create a sharp shock wave then, which is two-dimensional and therefore can be heard much further.
Now, with small particles like light, this issue doesn't arise, because the air doesn't need to get out of the way in the first place: at least visible photons don't interact with air much at all, so they simply “fly past”. When there is an interaction, it pretty much means just a single air molecule is hit by a photon. This gives it a slight “knock” but nothing dramatic. And in particular, it doesn't happen simultaneously along a whole front, so there's no reason a shock wave would build up.
1Another way to look at this is if you consider the gas on a molecular level. The molecules have a lot of thermal movement – the average speed is in the same order of magnitude as the speed of sound. On this microscopic level, sound propagation is basically a “chain of messengers”: one molecule gets knocked to be slightly faster or slower than usual. This extra momentum information is carried on not so much by the sound-wave movement, but by the random thermal movements – in a “smooth” way. Therefore a slow-moving object, or a sufficiently small object (like an alpha particle) only causes normal sound waves. But it doesn't work like that if you hit the air on a whole front at faster than the speed of sound: in this case, the forward momentum you impart is larger than the usual thermal movement, and you get supersonic behaviour.