acousticsmaterial-science
It's a well known fact that a sonic boom from something such as concord can shatter glass. I'm interested to know why a human is seemingly fine in the presence of the shockwave and yet the glass is completely destroyed?
EDIT: Rephrased: Why is glass the only or one of the only materials that actually completely shatters in the presence of a sonic boom?
The flash seen in this video may not be the glow of initial entry since the camera angle is angled somewhat along the path of the meteor; it is likely the active burning after the meteor has already entered the atmosphere. The mesosphere begins about 50 km above the earth's surface. However, the speed of sound in this region is a bit lower than the speed of sound on earth's surface, ranging between $280\text{m/s}$ and $330 \text{m/s}$. Coupled with the fact that we continue to hear less intense popping sounds for more than two full minutes afterwards suggests that the large boom heard is the shock wave, while the following sounds are actually from earlier events.
Meteors tend to enter the atmosphere at between 20 and 50 km/s, although they may be slower or considerably faster than this. This means that if their journey were straight down through the atmosphere, rather than across it, the trip would take 2 seconds or less. The trajectory of the meteor across the sky illustrates that it is a more glancing impact. The fact that the first sound takes 140 seconds to reach the camera indicates that the meteor is about 45 km from the camera. This is not reflective of the height of the meteor, but the absolute distance of the meteor path from the camera. There are estimates that the breakup altitude is around 20km. The following two minutes of reports reflect a linear distance of about 40 km of travel ($120\text{sec}\times300 \text{m/s}=40 \text{km}$), which probably took the meteor about 2 seconds to cover. So what we hear afterward is like a slow motion recording of the meteors breakup history, slowed down by a factor of somewhere between 40 and 100 times. If we could have heard these breakups in a frame comoving with the meteor, it would have sounded nearly like a single, continuous explosion. The first and loudest boom we hear is likely not from initial entry, but rather the sonic boom from the meteor's closest approach to the camera.
According to the American Meteor Society, the sonic boom of an asteroid or meteor (sometimes referred to as a 'fireball') is due to
If a very bright fireball, usually greater than magnitude -8, penetrates to the stratosphere, below an altitude of about 50 km (30 miles), and explodes as a bolide, there is a chance that sonic booms may be heard on the ground below. This is more likely if the bolide occurs at an altitude angle of about 45 degrees or so for the observer, and is less likely if the bolide occurs overhead (although still possible) or near the horizon.
And from CalTech's CoolCosmos page
When an object travels faster than the speed of sound in Earth's atmosphere, a shock wave can be created that can be heard as a sonic boom.
The reason for asteroids causing sonic booms in the lower atmosphere, is according to the article How the Falling Meteor Packed a Sonic Punch (Klotz, 2013) is due to
Because the meteor is supersonic, the waves, which travel at the speed of sound, can’t get out of the way fast enough. The waves build up, compress and eventually become a single shock wave moving at the speed of sound.
Looking a bit further in to what a sonic boom (Using a jet as an example) is and how it occurs is illustrated in the following diagram
So, if a meteor, asteroid is going faster than the speed of sound for particular part of the atmosphere, then a sonic boom will occur. Going back to the American Meteor Society's description of the likely cause of a sonic boom, they stated that if a meteor comes in
below an altitude of about 50 km (30 miles)
then a sonic boom is likely to occur, one of the reasons is that the speed of sound is slower, due to the temperature of the atmosphere at that height and lower. Below is a graph showing the speed of sound plotted against temperature as a function of atmospheric elevation:
Best Answer
The effect you noticed is a function of strength and size.
When you have a large window, and a sonic boom comes along, a relatively small pressure difference can set up very large tensile forces in the surface of the glass (especially if the shock wave cannot easily "go around the back" of the glass). When there is a bending stress, all you need is a small (surface) crack to act as a stress concentrator and you will get crack initiation: and once the crack is initiated, it will propagate as long as the stress is maintained*).
This very simplistic answer shows there are several differences between windows and humans:
The notable exception to all the above is the ear: there is an enclosed air pocket behind your ear drums, and the ear drum will move violently back as the shock wave hits. This can do permanent damage to the structure of the ear, including rupture of the ear drum.
When people go scuba diving, they can be subjected to pressures that is many times greater than atmospheric pressure - yet they survive. It's not the pressure that kills, but the pressure difference. Humans "equalize" quickly - ears and sinuses are possible exceptions. Incidentally, when divers try to surface quickly, they have to make sure to breathe out continuously or they will rupture their lungs (as a pressure difference would build up between lungs and surroundings).
None of the above is meant to imply that it is not possible to create a shock wave that can damage human tissue; but the combination of compliance, size and toughness means that a glass pane will shatter rather easily compared to more diffuse damage in human tissue (at sufficiently high pressure levels).
*) Specifically, the fact that the glass will first bend and store elastic energy means that once the critical stress is reached (which is a function of surface condition and possible built-in stresses) a lot of energy is available / released quickly, resulting in acceleration and branching of the cracks and (frequently) complete disintegration. For some glass, this is a deliberate effect: during manufacturing the glass is tempered in such a way that internal tension is built up and the outer surface is under compression. This raises the threshold before cracks will initiate (for that, the surface has to be in tension); but once it reaches that threshold, the crack, propagating into the center of the glass, encounters material that is already in tension. This makes the crack accelerate and bifurcate. The result is that the glass breaks "completely". You are less likely to be hurt by many small pieces of glass than a single big one, because the small pieces will have less momentum.