Eli5 air hose makes a visible ‘shock diamond’


So, I know it’s not an actual shock diamond. I couldn’t find the name of the phenomena or anything else through Google. My hypothesis is that the air is leaving the hose nozzle with enough force and velocity to compress the air ahead of the stream faster than it can be displaced, causing a high pressure spot that diffracts light differently and this being visible. ‘shock diamond’ is about 2mm diameter and appears acorn-like in shape, acorn cap facing the nozzle. Is there a name of this phenomena and if so could someone long me a photo or video showing some examples.

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You have the right idea. When light is passing through different materials, at the moment of the change (eg: air to water) the angle of the light changes. This is called refraction.

Dense air into thin air has the same effect. That’s what causes the mirage effect where a road appears to have water on it and the water disappears as you get closer. Very hot road surfaces heat up the air and light bends as it passes through that, resulting in you looking down at the road but actually seeing a bit of the sky. Not reflected, but light actually turned as it approached the road.

Compressed air would be the same sort of effect, only the air is thicker rather than thinner in a spot.

It’s probably condensation: When the air exits the nozzle and decompresses, it rapidly cools down. This can cause the moisture in the air to concensate into tiny droplets that vaporize again as they mix with the surrounding air.

They definitely can be actual shock diamonds. It takes a surprisingly low pressure differential to get air to go supersonic…your average 100psi air hose is more than capable of pulling it off (you only need about 30 psi to get supersonic at normal conditions).

Popular Science did an article with links to cool videos about doing this with bottle rockets, which are just compressed air power: