163 votes

Can ants walk on liquid 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 ...
Ian_Kinner's user avatar
137 votes

Do the weights of two liquids not add when mixed?

Of course, by common sense, if you put together two objects with masses $m_1$ and $m_2$, and nothing comes out, then you end up with mass $m_1 + m_2$. Weights are a little more complicated because ...
knzhou's user avatar
  • 102k
91 votes
Accepted

Why does a floating object displace more substance than a sunk object?

When submerged, the coin displaces as much water as it has volume (logical). When floating on the box, the coin displaces as much water as corresponds to its weight. As metal has a higher density than ...
planetmaker's user avatar
  • 1,029
86 votes

Given that ice is less dense than water, why doesn't it sit completely atop water (rather than slightly submerged)?

When put in water, an objects sinks to the point where the volume of water it displaces has the same weight as the object. Archimedes was the one who discovered this. When you put lead in water, the ...
hdhondt's user avatar
  • 10.9k
64 votes
Accepted

What is the energy source if a tall water tank is used to transfer floating objects upwards instead of cables with motors?

The work you need to do (to insert the log) against the pressure of the fluid at that depth is equal to the work done by the fluid to get the log up to the height you desire. If you consider a log ...
Hritik Narayan's user avatar
62 votes
Accepted

Can ants walk on liquid mercury?

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 ...
Physical Mathematics's user avatar
59 votes
Accepted

Why do rotten eggs float in water?

The domestic chicken's egg shell has about 7000 pores that allow the embryo to breathe. When an egg rots the yolk and surrounding materials decompose and they give off gasses which can pass through ...
Adrian Howard's user avatar
55 votes

Can a battleship float in a tiny amount of water?

Yes it floats. And it has displaced its "own weight of water" in the sense that if you had filled the container with water and only then lowered the ship into the container, nearly all that water ...
mike stone's user avatar
  • 52.5k
54 votes

Is it correct to say that "WE" feel only 5/140 of the actual weight of brain as buoyancy acts on brain due to cerebrospinal fluid?

Try not to be too pedantic with the biologists. They have our medical health to worry about. What is most likely that they are really trying to convey but failed to precisely state, is that if the ...
naturallyInconsistent's user avatar
53 votes

Given that ice is less dense than water, why doesn't it sit completely atop water (rather than slightly submerged)?

I like to answer by reinterpreting your question: if you expect the ice to be completely atop the water because ice is less dense than water (as indicated in your left image), then you would also ...
bers's user avatar
  • 691
52 votes

Will a penny ever stand still in the water at a certain depth?

The answer is no. Water, being a liquid, is nearly incompressible, meaning that the density changes very little with increasing pressure. In the very deep ocean, the pressure can approach $10^{8}$ ...
Buzz's user avatar
  • 16k
42 votes

Why does a fluid push upward on a body fully or partially submerged in it?

The fluid does not really exert an upward force on a body. It exerts a force everywhere on the body normal to its surface. [Adapted from Hyperphysics] In a gravitational field, the pressure ...
RC_23's user avatar
  • 8,910
41 votes
Accepted

Why do we need to apply more force to push a submerged object deeper?

The force required to push an object into water increases as the object submerges, i.e. as the amount of water the object displaces steadily increases. But I think if you do the experiment carefully ...
Selene Routley's user avatar
39 votes
Accepted

Why do we feel weightlessness in water but not on land?

This is less of a physics question and more of a neurophysiology question. Physically, as you have noted, both the proper acceleration (measured by an accelerometer) and the coordinate acceleration ...
Dale's user avatar
  • 97.9k
35 votes

Will a penny ever stand still in the water at a certain depth?

Yes, it will, but in a different way than one might imagine. In the Earth's oceans it is definitely impossible. From the phase diagram of water, one can see that assuming a constant temperature of 300 ...
Martin 'Kvík' Baláž's user avatar
33 votes

Why do rotten eggs float in water?

It doesn't need to be rotten. When the egg is getting old, it evaporate water and looses mass while drying. Even if not rotten.
Camion's user avatar
  • 555
32 votes

Do the weights of two liquids not add when mixed?

@knzhou supplied a good answer. I’m going to offer a couple of other interpretations. The first has nothing to do with the fact that you’re mixing liquids—it’s just that there are difficulties in ...
Ben51's user avatar
  • 9,684
31 votes

Given that ice is less dense than water, why doesn't it sit completely atop water (rather than slightly submerged)?

I think the real question you're asking here is: why do less-dense fluids completely stay above more dense fluids, whereas less-dense solids partly sink? If the ice covered the same area as the water ...
leftaroundabout's user avatar
29 votes
Accepted

Can a submerged object in a free falling fluid sink faster than falling?

I want to supplement Emilio's intuitive answer discussing what would happen with some thoughts as to why what you propose in your second part cannot happen. What kind of object could fall out of ...
BioPhysicist's user avatar
  • 56.1k
28 votes
Accepted

Does an object float more or less with more or less gravity?

The object would actually float exactly the same for both values of $g$. Let $V$ be the volume of the body, $d$ its relative density, and $V'$ be the volume inside water. Then for equilibrium of the ...
Amritansh Singhal's user avatar
24 votes

Which weighs more in atmosphere, $1\,{\rm kg}$ of steel or $1\,{\rm kg}$ of feathers?

Feathers are made from keratin, with a density of about $1.3\ \mathrm{g/cm^3}$. The net volume displaced by a kilogram of feathers is then $751\ \mathrm{cm^3}$. Steel has a density of $7.86\ \mathrm{g/...
niels nielsen's user avatar
23 votes
Accepted

Can a ship float in a (big) bathtub?

Yes a ship can float in a big bath tub with very little water. No you do not need as much water as the weight of the ship. In theory, you can use less than a cupful! Image from B5-2. How much water ...
sammy gerbil's user avatar
  • 27.2k
23 votes
Accepted

Why does a helium balloon rise?

The buoyant force* depends on the volume of the object (or at least the volume of the object submerged in the fluid) and the density of the fluid that object is in, not necessarily/directly on the ...
BioPhysicist's user avatar
  • 56.1k
23 votes

Can a submerged object in a free falling fluid sink faster than falling?

The Equivalence Principle tells you that physics in free-fall is identical to physics in an inertial frame in the absence of gravity, in which case there is no buoyancy and any changes to the boundary ...
Emilio Pisanty's user avatar
22 votes

Why does a floating object displace more substance than a sunk object?

The coin is denser than water. When placed on the box, it will displace it's weight in water, which is more volume than the coin. When placed directly in the water it will sink to the bottom and ...
Jason Goemaat's user avatar
21 votes

Can a battleship float in a tiny amount of water?

Note that the water does not need to have been present - this calculation gives just the way to calculate the non water volume occupied by the floating object (that hence is unavailable for water). ...
Has QUIT--Anony-Mousse's user avatar
21 votes

Why does a helium balloon rise?

The high-level explanation is "buoyancy". If you want to know the actual mechanism, it's that the pressure in a fluid increases with depth: the air pressure at the top of a balloon is slightly lower ...
Acccumulation's user avatar
21 votes

Why do we feel weightlessness in water but not on land?

Do you feel weightless when floating on water? I don't. I feel that the water is carrying me. I can feel how gravity pulls me down while the buoyancy force holds be up. Just like my soft mattress is ...
Steeven's user avatar
  • 50.5k
17 votes

Does hot air really rise?

Buoy, does it ever. To contrast the previous answers I will give a mathematical description and a concrete example to bolster the intuitive understanding. Ideal Gas Law From thermodynamics we know ...
NauticalMile's user avatar
17 votes

Do the weights of two liquids not add when mixed?

Based on your question I assume the precision is very important in your lab. If so, then yes, your colleague is right. At least to some degree. There are main three possibilities why this may happen. ...
Ister's user avatar
  • 521

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