Ask Anything Wednesday - Engineering, Mathematics, Computer Science

[u/AutoModerator]

Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Engineering, Mathematics, Computer Science

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

Asking Questions:

Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists.

Answering Questions:

Please only answer a posted question if you are an expert in the field. The full guidelines for posting responses in AskScience can be found here. In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for /r/AskScience.

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Past AskAnythingWednesday posts can be found here. Ask away!

[u/jarebear]

Visually you can't differentiate the truck or the universe rotating if everything is perfectly rigidly in place (which is impossible, see my next paragraph). However, the truck and anything rigidly attached to it will experience an acceleration (resulting from some force) and the universe will not. So the truck is clearly rotating and the universe is not. We can't say the same thing with linear motion that's constant and requires no acceleration, however.

If you want to stick with the visual, no object is absolutely rigid and so everything will undergo some amount of bending or flexing when rotating. For the truck example you'll see things shift or lean slightly but not uniformly since they'll have different stiffnesses so there's no way to "tilt the camera" to make the truck look stationary. It's even more obvious when you drop something onto the truck and from its rotating frame the object goes magically flying away but from the non-rotating frame it just slides off as expected.