I know it comes from breaking the sound barrier, but why a boom instead of complete silence?
I have the understanding it creates a physical wave too.
Bonus questions: Does the pilot hear it?
Can the same thing be achieved underwater?
Related: I know the speed of sound is faster under water, does any reaction happen theoretically at the air speed of sound underwater?
In: 310
As a jet speeds up, it builds a wave in front of it – similar to a boat. At certain speeds/elevations/atmospheric conditions, the jet can pass through that wave, which creates an explosion of sorts. The jet is outrunning the bulge of sound being pushed in front of it. And breaking through creates a shockwave. And nope – as far as I know, pilots say there’s no noticeable change when they pass through Mach 1.
For every inch a jet (or anything really) moves forward, it pushes the air in front of it forward in the form of a small wave of higher pressure air. Similar to shaking a slinky, that wave travels forward in front of the jet at the speed of sound, since that small wave of pressure is *the sound of the jet itself*.
What happens then when a jet travels faster than the speed of sound? The wave in front of it can’t move faster than the jet, so instead of a sound wave which is comprised of a bunch of “ripples,” all the ripples bunch up on top of each other and we get one massive “shock wave,” which is essentially one really big and loud wave of pressure. It’s basically the same thing that happens when an explosion goes off. You can visualize this yourself in a swimming pool: Place your arm vertically through the surface of the water, and then move your arm very slowly and you’ll see ripples moving in front of your arm, however if you move your arm very quickly, the ripples instead bunch up and form a big wave form a big wave.
Since the jet keeps moving, it keeps pushing air out of the way and therefore continues to make a shock wave as it travels through the air. The “boom,” you hear is simply the sound from the jet passing in front of you at that moment (or in reality a few moments ago) and the people further along the jet’s path will hear the shock wave later, since the jet is constantly making the noise.
As for underwater, it would technically be possible and the exact speeds would be dictated by the speed of sound in water, though actually getting something to those speeds would be difficult without the object destroying itself.
Have you ever had a stereo turned up so loud you could feel it in your ear Le and your torso? That’s the wave pressure of the sound.
When a craft moves faster, that wave is being dragged along the skin of the craft, so that it builds up into a BIG wave before (continually) falling off the back; making a constant roar. From the ground, it’s a boom as it passes because the plane is moving.
The pilot doesn’t hear the boom; he’s moving faster than it and always ahead of it. Much like a ship in orbit doesn’t hit the ground because it’s moving so fast that it misses.
It _could_ be done underwater! However, water is very very dense; and it takes much more energy to accelerate through water. There is a theory that may have engineering application such that a torpedo is covered with tiny holes, and continually pushes out high-pressure steam to reduce its drag, and therefore move faster than sound in water.
Sound.
When you move through the air, you create a sound. At low speeds, it’s impossible to hear, but at high speeds, it’s much more noticeable. Add in a jet engine making noise, and it’s even louder. When you travel at or above the speed of sound, you create sound waves that travel in the same direction as you, but behind you, meaning that as you continue, you have more and move sound waves stacking up in that wave front behind you. This is a sonic boom.
The pilot cannot hear anything aside from sounds in the plane itself or in front of the plane, not the sonic boom.
This is possible to do in water, but it’s much harder. The speed of sound in water is about 5x that of the speed of sound in air, so you’d have to travel 5x the speed through a medium that has more drag to do it. If you did succeed, you would also be able to see a vacuum bubble behind you, since the water wouldn’t be able to fill that space before you leave it. It also creates an insane amount of heat.
Also, nothing special happens in water at air’s speed of sound.
We can get particles to travel through water faster than light can travel through water, and it creates a light boom which we see as a blue glow called cherenkov radiation. The speed limit in physics is the speed of light in a vacuum, so traveling faster than the speed of light in water is perfectly fine.
Aerodynamicist here.
Imagine standing on the shore of a lake and watching a boat go by. As the front of the boat pushes through the water, it creates a bow wave. That wave then “propagates” away from the boat to both sides. If you were to look straight down on the boat from above, the bow wave would look like a V-shape. As long as the boat is moving, the bow wave is continuously forming at the bow and then moving away to the sides.
https://en.m.wikipedia.org/wiki/Wake_(physics)#/media/File%3AFjordn_surface_wave_boat.jpg
If you’re standing on the shore, sometime after the boat goes by, it’s bow wave will eventually propagate far enough to reach your position. You’ll know it because the gentle lapping waves on the shore will be replaced by big splashy waves for just a moment, then calm back down.
Now think of the airplane pushing through the air. Just like the boat, the nose tip of the plane creates a bow wave. On a slow airplane, the bow wave is a gentle ripple of many small waves as the air gets nudged away, just like the boat. But when a plane goes supersonic, the air can’t move out of the way fast enough, so all the waves coalesce into a single big wave called a “shock”. But the shock wave is still essentially like the bow wave from the boat, and it propagates out in a V shape just the same.
https://en.m.wikipedia.org/wiki/Oblique_shock#/media/File%3AShockwave_pattern_around_a_T-38C_observed_with_Background-Oriented_Schlieren_photography_(1).jpg
And just like at the lake, the shock wave from the nose of the airplane will propagate all the way to where you are on the ground. As it passes over you, your ear will perceive the wave in the air as a loud and sharp sound, aka a sonic boom.
From this concept, incomplete as it is, you’ll be able to avoid a couple of common misconceptions. For one, a sonic boom isn’t a single event that occurs at the moment a plane transitions from subsonic to supersonic. Any time an airplane is traveling at supersonic speeds, it is dragging a sonic boom behind it continuously just like the boat and the bow wave. The other is that the pilot never hears it. To hear it, the wave has to pass over your ear when the plane passes, but the pilot is traveling at the same speed as the rest of the aircraft (at least he’s supposed to be), so it never sweeps over him the way it does people on the ground.
The jet, or whatever is breaking the sound barrier is essentially creating a complete vacuum behind it. The air cannot travel faster than the speed of sound. This means as the jet moves it pushes the air outward but the air is now moving at the speed of sound inward and the jet is long gone. The sound is air clapping together as it hits itself at the speed of sound.
Sound is literally preasure waves moving through the air, sonic booms are when a ton of these pressure waves end up stacking on top of each other combining their aplitude and thus their perceived volume by us.
In other words one Giant sound wave is literally one giant preasure wave. Giant preasure waves can move or damage things
Its the charging thats builds up by holding back for 1.5 seconds and going foward before pressing jab fierce or strong. Incredible zoning tool.
“light” is traveling way faster than the speed of sound. why doesn’t it make a boom?
Also, I just want to add, sonic booms arent one sound that happened at some point.
It is a continuous sound that is created by the vehicle, and you just hear a boom when it passes by you.
Latest Answers