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electric_ionland t1_izs4cv3 wrote

Replying to SS7Hamzeh (#905,935)

This answer was generated by a GPT style bot, the user has been banned. Please see our policy about that kind of bots here:https://www.reddit.com/r/askscience/comments/zg4sgl/meta_bots_and_ai_tools_on_raskscience/

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RobusEtCeleritas t1_izsbk7v wrote

The speed of sound is the speed at which infinitesimal oscillations in the density and pressure propagate through the fluid.

If an object moving through the fluid at or above the speed of sound, there's no way for any of the fluid upstream of the object to "know" that the supersonic object is coming.

And as a result, in order for conservation of mass, momentum, and energy to be upheld, you find that there must be discontinuities in the density, pressure, etc. at some point between the fluid upstream of the object and the fluid downstream of the object. These discontinuities are called shocks, and they first start to form specifically as the object reaches the local speed of sound.

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gramoun-kal t1_izt7szd wrote

When something noisy is coming towards you, the noise gets louder and louder, until the thing passes nearest you (it's loudest then) and then it gets less and less loud

Now, if that thing is going faster than sound, you won't hear it coming. The thing travels faster than its own noise. There is no noise build-up as it approaches. Then it passes you, and the noise level goes from 0 to loudest all at once. One second later, the thing is hundreds of meters away and way less noisy. So it should like a thunderclap. The sonic boom.

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cuicocha t1_izv04fo wrote

Replying to Psyese (#909,174)

A shock is a significant discontinuity in pressure, density, and velocity. Viscosity means that nothing is truly discontinuous, so in sea-level air, "discontinuous" means a big jump in a distance of approximately microns.

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DisasterousGiraffe t1_izx35l6 wrote

Replying to nassau4 (#906,439)

The speed of sound is the speed at which changes in pressure move through the air.

If a bullet is shooting through the air faster than the speed of sound it is said to be "supersonic". (The word "supersonic" literally means above, indicated by the Latin word "super", like "superior", stuck on the front of the word "sonic" meaning sound. "Sonic velocity" means at the speed of sound, and "subsonic" means below the speed of sound, Latin word "sub" meaning below stuck on the front of sonic, like submarine is below the surface of the sea.) A supersonic bullet is moving faster than the sound pressure changes move through the air. So you will not hear the bullet before it hits you.

All the energy in the sound pressure changes that are not going forward from the supersonic bullet has to go somewhere else instead. The pressure changes go into sharp changes in pressure between the air in front of the bullet and the air behind the bullet. These sharp changes in pressure are called "shocks", and they happen when the bullet reaches the speed of sound. Subsonic bullets do not create shocks because the energy can move forward in front of the bullet - you will hear a subsonic bullet before it hits you.

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zekromNLR t1_j007zm4 wrote

Replying to xratedcheese (#908,116)

The speed of sound in water is nearly five times as fast as in air, about 1500 m/s. An object moving that fast through water would experience a dynamic pressure of about 1.1 GPa, compared to about 70 kPa for something moving at the speed of sound through sea-level air - in other words, not really possible outside of extreme scenarios like meteorite impacts.

But yes, there would be a sonic boom. You can with a fast enough impact even have a sonic boom in solid materials.

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