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I'm not a physicist, but I was wondering:

Can ants walk on dense liquid like mercury and why?

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closed as off-topic by AccidentalFourierTransform, Kyle Kanos, David Z Jul 12 '18 at 9:41

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    $\begingroup$ Here is a video of a spider walking on mercury. $\endgroup$ – user27542 Jul 11 '18 at 16:20
  • $\begingroup$ Tangentially related, but this xkcd What-If gives a brief overview of liquid Mercury's denseness: Steel ball bearings float on the surface, and you'd have to lean your body weight into an oar to get it to break the surface. $\endgroup$ – Robotnik Jul 12 '18 at 6:23
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    $\begingroup$ @Apolo I'd suggest editing your question to ask for the theory behind the answer, then. Doing that could easily make it on topic. What would be particularly useful to include is a brief explanation of why you think ants shouldn't be able to walk on liquid mercury. $\endgroup$ – David Z Jul 12 '18 at 10:05
  • $\begingroup$ An interesting discussion about whether this question is on-topic has been moved to chat. Please use further comments to suggest improvements to the question. $\endgroup$ – rob Jul 12 '18 at 20:39
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Whether or not a small animal/insect can walk on a liquid is determined much more by surface tension than by density. To see why this is consider a dense liquid without any surface tension. You would float in it very well, but if you tried to walk on it you would step right through the surface and fall over, sinking until you were sufficiently submerged to float (the amount of liquid displaced is equal to your body weight). Now imagine a very high surface tension liquid that is not very dense. You would be able to walk across it as long as you don't break the surface. The second you break the surface you would sink like a stone.

So now for the ant in mercury. The surface tension of mercury is much higher than that of water (~6x), so I think it's safe to say that an ant might succeed in walking across the mercury for a short while, as some insects of similar mass can walk along water. Though without some coating on the ants feet which repelled to mercury (like water-walking insects have for water), the ants feet would likely get covered in mercury and would start sticking the surface of the liquid.

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    $\begingroup$ If the ant did break the surface tension, its buoyancy would mean that only some small fraction of its body would end up submerged. You could imagine an ant "walking on mercury" by having part of its abdomen submerged and propelling itself with its legs. Of course, you could imagine a human doing this too; we'd just be more likely to call it "swimming" in our case. $\endgroup$ – Michael Seifert Jul 11 '18 at 14:44
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    $\begingroup$ It seems like mercury doesn't wet most common materials (including human skin), probably because of its high surface tension. So, I guess, ants don't need any special coating to avoid getting covered in mercury. $\endgroup$ – user27542 Jul 11 '18 at 16:15
  • $\begingroup$ "as some insects of similar mass can walk along water" I think it's a matter of mass per area, so mass alone doesn't say enough. $\endgroup$ – Mast Jul 11 '18 at 17:45
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    $\begingroup$ Mass per contact area with the liquid is what should matter, but water-walking bugs don't have giant feet, so as a reasonable approximation, I think it still makes some sense to say ants should be able to walk on mercury, it has a lot higher surface tension. $\endgroup$ – Keefer Rowan Jul 11 '18 at 18:10
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Ants can walk on mercury

Needing any excuse to break away from the work I was doing, I immediately assumed the task of answering this question.

Yes, ants can walk on mercury with no trouble at all. I bet it was even kind of fun, but this little punk just split as soon as possible. I got a video, but had to settle for a screenshot for this post.

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    $\begingroup$ Well there is nothing like trying it out! Btw is mercury poisonous to ants? You could add a "No ants were harmed in the production of this video" disclaimer in the end then. $\endgroup$ – Orphevs Jul 12 '18 at 11:39
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    $\begingroup$ It's worth noting that this answer doesn't offer any explanation at all. $\endgroup$ – user191954 Jul 12 '18 at 13:40
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If you'd like to learn a little more about mercury, the popular youtuber Cody'sLab has done several videos on it-

He successfully stands on a bucket of mercury in this one, although it looks like walking would be impossible.

He successfully drives an RC car on mercury in this one and concludes that one would be able to drive a full-sized car on a lake of mercury as well.

Based off the intuition of mercury's buoyancy apparent in these videos, I would expect that ants would be able to walk on mercury.

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