Use "buoyancy" for any question where an object is suspended or submerged in a fluid. Buoyant force is the force that acts upward on a partially or completely submerged object.
Questions tagged [buoyancy]
700 questions
124
votes
9 answers
Why does a helium filled balloon move forward in a car when the car is accelerating?
I noticed that when I had a helium filled, latex balloon inside of my car, it moved forward in the cabin as I accelerated forward. The faster I accelerated forward, the faster the balloon went from the back of the car to the front of the car. The…
user33986
- 1,209
86
votes
7 answers
Which way does the scale tip?
I found the problem described in the attached picture on the internet. In the comment sections there were two opposing solutions. So it made me wonder which of those would be the actual solution.
So basically the question would be the following.…
Peter Raeves
- 973
78
votes
9 answers
Why does ice melting not change the water level in a container?
I have read the explanation for this in several textbooks, but I am struggling to understand it via Archimedes' principle. If someone can clarify with a diagram or something so I can understand or a clear equation explanation that would be great.
stackseverywhere
- 929
77
votes
5 answers
Do the weights of two liquids not add when mixed?
I was given an interesting dilemma today. A co-worker saw me adding a liquid (Diisopropyl ethylamine AKA DIPEA) to a flask filled with another liquid (Tetrahydrofuran AKA THF). I needed to weigh out exactly 5 grams of DIPEA into the THF and so I…
Brian
- 687
58
votes
8 answers
Given that ice is less dense than water, why doesn't it sit completely atop water (rather than slightly submerged)?
E.g.
If we had a jar of marbles or something else of different densities and shook it, the most dense ones would go to the bottom and the less dense ones to the top.
(Image Source)
If I put a cube of lead in water it would sink all the way to the…
K-Feldspar
- 1,377
56
votes
3 answers
Why doesn't this perpetual motion machine using the buoyant force work?
I realize this isn't possible, but I can't see why not, especially if you change the model a little bit so that the balls simply travel through a tube of water on the way up, rather than exactly this model.
Please be clear and detailed. I've heard…
Martin
- 579
47
votes
6 answers
Why do rotten eggs float in water?
My mom told me that one can check whether an egg is rotten by sinking it in a glass of water. If it floats, then it is rotten.
I didn't find any explanation for this phenomenon. If anyone knows one, please answer.
prAnjal
- 593
42
votes
4 answers
Will a penny ever stand still in the water at a certain depth?
Let’s say I drop a penny in the deepest part of the ocean having a certain depth. Would the penny become buoyant enough to stand still in the water, since the density of water increases with depth? Since the buoyancy of objects becomes greater as…
Justus Bozzi
- 445
41
votes
3 answers
Can ants walk on liquid mercury?
I'm not a physicist, but I was wondering:
Can ants walk on dense liquid like mercury and why?
Apolo
- 513
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39
votes
8 answers
Can a battleship float in a tiny amount of water?
Given a battleship, suppose we construct a tub with exactly the same shape as the hull of the battleship, but 3 cm larger. We fill the tub with just enough water to equal the volume of space between the hull and the tub. Now, we very carefully lower…
SlowMagic
- 1,053
38
votes
2 answers
Basic buoyancy question: Man in a boat with a stone
This comes from a brain teaser but I'm not sure I can solve it:
You are in a rowing boat on a lake. A large heavy rock is also in the boat. You heave the rock overboard. It sinks to the bottom of the lake. What happens to the water level in the…
lezebulon
- 483
35
votes
4 answers
What is the energy source if a tall water tank is used to transfer floating objects upwards instead of cables with motors?
Suppose I want to transport some logs from the ground to the roof of a tower. Originally I can use a lift, or some cables, or even move the logs upwards manually; then the energy is converted to the potential energy of logs.
Now, if I build a tall…
Gstestso
- 917
34
votes
4 answers
Why does a cork float to the side of a glass?
Why does a cork ball float to the side of a glass as illustrated in the following GIF? What is the physical phenomenon behind this observation and why does it happen?
Mohammad Fakhrey
- 839
31
votes
5 answers
Why does a floating object displace more substance than a sunk object?
Consider a box floating on water having a coin on top, now suppose after some time by some external influence, the coin is dropped into water. After doing the calculations, to my surprise, I found that the water level actually drops...I just can't…
Clemens Bartholdy
- 8,309
28
votes
16 answers
Does hot air really rise?
"Heat rises" or "warm air rises" is a widely used phrase (and widely accepted phenomenon).
Does hot air really rise? Or is it simply displaced by colder (denser) air pulled down by gravity?
jasonmklug
- 445