That's absolutely happening here - it's a really good practical example of the speed of sound. It doesn't really take much distance for the effect to be noticeable - I was in marching band in high school and when we were spread out across a football field it was *really* important we pay attention to the conductor, or everything would end up sounding super muddled to the audience.

The crack at the end of this and other whips when correctly used, is actually a sonic boom, as the very end of the whip is moving faster than the speed of sound.

Works with most hot liquids with powders, I think I first noticed it in a mug of instant hot cider......

https://en.m.wikipedia.org/wiki/Hot_chocolate_effect

The hot chocolate effect, also known as the allassonic effect, is a phenomenon of wave mechanics first documented in 1982 by Frank Crawford, where the pitch heard from tapping a cup of hot liquid rises after the addition of a soluble powder. It was first observed in the making of hot chocolate or instant coffee, but also occurs in other situations such as adding salt to supersaturated hot water or cold beer. Recent research has found many more substances which create the effect, even in initially non-supersaturated liquids.
It can be observed by pouring hot milk into a mug, stirring in chocolate powder, and tapping the bottom of the mug with a spoon while the milk is still in motion. The pitch of the taps will increase progressively with no relation to the speed or force of tapping. Subsequent stirring of the same solution (without adding more chocolate powder) will gradually decrease the pitch again, followed by another increase. This process can be repeated a number of times, until equilibrium has been reached. Upon initial stirring, entrained gas bubbles reduce the speed of sound in the liquid, lowering the frequency. As the bubbles clear, sound travels faster in the liquid and the frequency increases

66 miles. that's over an hour drive at the highway speed limit.

sound of the hawk in this ad is a red-tailed hawk cry.

https://youtu.be/lP0BPc023qg?t=30

that trumps id'ing an elephant picture.

Everything I've read about the SR-71 in the past seems to support the idea of expansion gaps being designed into the panels due to the amount of heat created from flying 3x the speed of sound.

If you want the timing, instead of a camera, why not just use a microphone, time the length between clicks. Adjust for the speed of sound if you need to be really precise.

Counter-rotating propellers sparked my curiosity when I first saw them on a British Seafire Mk46 at a flight show in the early nineties.

So my amateur's answer would be that it's about the problem of turning the engine's power into thrust. With increasing power, you can either increase the propeller's RPM or its area. So you either a) spin it faster, b) increase its diameter, c) use a more favourable blade geometry, d) add more blades.

a) and b) both lead to blade tips moving faster, and once they approach the speed of sound, wave drag sets in and ruins your day. b) also runs into issues in terms of ground clearance. Thus the Kim Jong-un blades on planes like the An-70: short and fat.

c) is rather difficult to do in terms of manufacture -- that's why more pronounced blade shapes are a relatively recent development.

d) on a single propeller decreases the efficiency of each blade as it passes through the previous blade's vortex. That's why, for instance, German planes in WW2 almost exclusively relied on 3-bladed propellers with increasing blade size, whereas Supermarine went to four and even 5 blades rather quickly. You can work the issue to a certain degree by modifying the blade geometry, thus the 8 blade props on a modern A400M.

Adding more blades by adding another propeller gets around d), although the aft prop still loses efficiency compared to the front prop. On the other hand, counter-rotating props massively reduces problems with torque, which can be rather horrendous for single engine prop planes. The Bf 109, for instance, is (in)famous for being difficult during take-off as it pulls to the side quite violently.

Underwater tunnels dont need a complex solution sitting behind them to maintain that pressure.
Underwater tunnels arent open to the air, where retards can shoot at them.
Water doesnt act like air in a decompression event like what thunderf00t is talking about....it doesnt travel at the speed of sound to fill the void..

Google tells me that the speed of sound in Pyrex is approx 5.5km/s. So pretty fast.

I think the X-1 is the first that could pass the speed of sound in normal level flight, without needing to dive to gain speed. That's my understanding at least. It ll depends how the record is stated though, it's almost certainly not the first manned craft to pass the sound barrier as you point out.

About 7 seconds for the shock wave to hit so, at the speed of sound, the blast was a little over 2km away?

Myth. Who could have been in a position to want to "put" something on a Blackbird and not known that planes can (and do) run into their own bullets already at speeds close to the speed of sound?

Powers always change depending on what books your reading, but the big difference is that Quicksilver can only move at the speed of sound, and the Flash can move at the speed of light.

The volcano is here - https://goo.gl/maps/LbKHf

They appear to be somewhere in the middle of the bay, which makes it about 4km (?) away. If you assume (like the yt commenters did) that the shockwave slowed to the speed of sound almost instantly you would calculate a distance of approx 4-4.5kms which would have them almost on the opposite shoreline (or even on land) which they clearly are not...

p.s. Yes I realise that a supersonic shockwave should cause you to underestimate rather than overestimate distances, perhaps they're really a bit further from Rabul than I assumed?

p.p.s They were staying at Kokopo Beach Bungalows, and went out on the boat for a better look.

so minimally that far... this was pretty good from wiki:

Shock waves form when the speed of a fluid changes by more than the speed of sound.[3] At the region where this occurs sound waves travelling against the flow reach a point where they cannot travel any further upstream and the pressure progressively builds in that region, and a high pressure shock wave rapidly forms.

Shock waves are not conventional sound waves; a shock wave takes the form of a very sharp change in the gas properties on the order of a few mean free paths (roughly micrometers at atmospheric conditions) in thickness. Shock waves in air are heard as a loud "crack" or "snap" noise. Over longer distances a shock wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air and loses energy. The sound wave is heard as the familiar "thud" or "thump" of a sonic boom, commonly created by the supersonic flight of aircraft.