this post was submitted on 20 Jul 2025
62 points (97.0% liked)

No Stupid Questions

42454 readers
818 users here now

No such thing. Ask away!

!nostupidquestions is a community dedicated to being helpful and answering each others' questions on various topics.

The rules for posting and commenting, besides the rules defined here for lemmy.world, are as follows:

Rules (interactive)


Rule 1- All posts must be legitimate questions. All post titles must include a question.

All posts must be legitimate questions, and all post titles must include a question. Questions that are joke or trolling questions, memes, song lyrics as title, etc. are not allowed here. See Rule 6 for all exceptions.



Rule 2- Your question subject cannot be illegal or NSFW material.

Your question subject cannot be illegal or NSFW material. You will be warned first, banned second.



Rule 3- Do not seek mental, medical and professional help here.

Do not seek mental, medical and professional help here. Breaking this rule will not get you or your post removed, but it will put you at risk, and possibly in danger.



Rule 4- No self promotion or upvote-farming of any kind.

That's it.



Rule 5- No baiting or sealioning or promoting an agenda.

Questions which, instead of being of an innocuous nature, are specifically intended (based on reports and in the opinion of our crack moderation team) to bait users into ideological wars on charged political topics will be removed and the authors warned - or banned - depending on severity.



Rule 6- Regarding META posts and joke questions.

Provided it is about the community itself, you may post non-question posts using the [META] tag on your post title.

On fridays, you are allowed to post meme and troll questions, on the condition that it's in text format only, and conforms with our other rules. These posts MUST include the [NSQ Friday] tag in their title.

If you post a serious question on friday and are looking only for legitimate answers, then please include the [Serious] tag on your post. Irrelevant replies will then be removed by moderators.



Rule 7- You can't intentionally annoy, mock, or harass other members.

If you intentionally annoy, mock, harass, or discriminate against any individual member, you will be removed.

Likewise, if you are a member, sympathiser or a resemblant of a movement that is known to largely hate, mock, discriminate against, and/or want to take lives of a group of people, and you were provably vocal about your hate, then you will be banned on sight.



Rule 8- All comments should try to stay relevant to their parent content.



Rule 9- Reposts from other platforms are not allowed.

Let everyone have their own content.



Rule 10- Majority of bots aren't allowed to participate here. This includes using AI responses and summaries.



Credits

Our breathtaking icon was bestowed upon us by @Cevilia!

The greatest banner of all time: by @TheOneWithTheHair!

founded 2 years ago
MODERATORS
 

I was watching an XKCD "What-If" video recently and Randal off-handedly mentions the title fact as a given. Upon a further Google search I see explanations about why sound moves faster in liquids than gasses but nothing for my specific question. Is there an intuitive explanation for that fact or is it just one of those weird observable facts with no clear explanation

you are viewing a single comment's thread
view the rest of the comments
[–] Fleur_@aussie.zone 11 points 4 days ago* (last edited 4 days ago)

Ahhh in terms of fluid flow? I mean you can move a glass of water as fast as you want (don't @ me physicists) if the glass is moving at that speed.

Assuming this is flow.

Let's think about a 1 metre long pipe full of water. Let's make the water start flowing though this pipe by pushing through the water at the start of the pipe. Now as water enters the pipe, water at the other end of the pipe exits. But there's a time delay between the first new water that enters the pipe and the first water to leave the pipe. (I can explain this further if needed) That time delay is the time it takes the speed of sound in water to travel through the 1m pipe.

Now let's consider water moving faster than the speed of sound in water entering the pipe. It's moving so fast through the pipe that it actually reaches the end of the pipe before the water at the end of the pipe has had enough time to move out of the way. Here flow is effectively dead and the water isn't really flowing though the pipe anymore, it's just being pushed through by whatever is moving the water in the first place.

At the end of the day it's semantics, you could define flow as being "water moving through a pipe" and in that case yeah, water can "flow" at whatever speed you want if you push it hard enough. Typically though, flow means a steady and consistent stream of fluid. And at supersonic speeds, that stream is anything but steady and consistent.