3 upvotes, 4 direct replies (showing 4)
View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
"Put two ships in the open sea, without wind or tide, and, at last, they will come together." - Jules Verne. Is this correct and if so, why?
Comment by x-seronis-x at 20/07/2022 at 19:01 UTC
5 upvotes, 1 direct replies
Yes. Gravity is the reason. With PERFECTLY zero wind or tide, basically zero forces acting on their acceleration in any direction, their own mass would act on each other over distance and slowly VERY SLOWLY draw them together.
Realistically the oceans might evaporate before they reach each other but we were already assuming zero outside factors for this to work at all.
Comment by SonOfOnett at 20/07/2022 at 19:57 UTC*
5 upvotes, 0 direct replies
This is a fun question. Ignore gravity and ignore physics for a moment. Consider two ships moving randomly across the seas in two dimensions (east-west and north-south). Now put a grid on the ocean with a really fine mesh, like each point is 1mm. Define each ships position on this grid and have them move randomly on it. The system can be modeled as a 2D random walk.
Interestingly, if we were talking about spaceships (3D random walk) there’s only about a 1/3 chance of them meeting again
There are lots of good books and articles about this, but also the quote “a drunk man will find his way home, but a drunk bird may get lost forever”
Comment by Indemnity4 at 21/07/2022 at 01:00 UTC*
3 upvotes, 0 direct replies
There is the metaphorical answer, and a physics answer.
There is a known boating phenomena where two boats moving in parallel (or static side by side) will always collide.
Bernoulli’s theorem shows that when velocity of liquid flow increases the pressure decreases. Air is also a fluid, as well as water.
When two boats come closer, there is an increase in the air-velocity between the narrow gap of the two boats. The pressure in *the gap between the two boats* is less than the pressure *on the outer surfaces of the boats*.
The same is true for the water between the boats. The velocity of water between the boats is getting squeeze/directed and moving faster the water on the outer sides of the boats. This creates a low pressure in the water that starts to suck the boats toward each other.
Therefore, they are pulled towards each other and may sometime also collide with each other.
Comment by DeepFriedBetaBlocker at 20/07/2022 at 18:48 UTC
2 upvotes, 0 direct replies
Yes, they exert their own gravitational fields (albeit MINISCULE, all objects do) but given enough time they will be attracted to one another until they touch.