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.

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Bouyant force in air on hollow object

I understand that the buoyant force is equal to the weight of the air displaced by the volume of the object. I also know that if we had a perfectly solid cube or a hollow cube closed on all sides so ...
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2answers
152 views

Reaction force for buoyancy?

According to Newton's 3rd law each force (action) has a counter-force (reaction). What is the reaction (counter-force) of buoyancy?
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3answers
968 views

The physics behind Balloons lifting objects?

Apologies for the super basic question, but we all have to start somewhere right? Can somebody please explain exactly how you would calculate the number of helium balloons it would take to lift an ...
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2answers
127 views

Why do Oreo crumbs float to a single glob at the very center in a glass of milk? [duplicate]

I had Oreos and milk a while ago and left my half-full cup of milk out on the counter. Afterwards I noticed that the crumbs had surfaced in a circular coin-sized glob, and just now I looked again to ...
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4answers
4k views

Why doesn't a tied balloon behave like a pendulum?

It is well known that a tied weight will oscilate under the effect of gravity if left from aside, like a pendulum. However, if we tie a helium balloon to the ground from and left it form the floor ...
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1answer
205 views

If hot air expands in all directions why is the balloon moving up?

A balloon is moving up. The hot air inside the balloon is expanding in all directions and cold air outside the balloon acts with force on the balloon from all directions (higher pressure force). Why ...
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2answers
155 views

Weight of solid partially immersed in water

Suppose a spherical object is kept in water and nine tenths of the object are inside the water, while the remaining tenth floats. Find the weight of solid inside liquid. By Archimedes' principle, ...
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1answer
154 views

Buoyancy / Drag Problem

Buoyancy / Drag Problem Just a little bit of help would be nice. I have a spherical particle of radius $R$ and density $\rho$, surrounded in a fluid of density $\phi$ and viscosity $\eta$. I'm ...
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2answers
207 views

Why is Buoyant Force $V\rho g$?

For a submerged object, buoyant force ($F_b$) is defined as: $$F_b = V_{\text{submerged}} \times \rho \text{ (density)} \times g \text{ (gravitational constant)}$$ Conceptually, the buoyant force ...
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1answer
832 views

How to calculate the buoyant force on a balloon at different altitudes [duplicate]

For a project into balloon simulation I'd like to know how the force on a balloon changes with altitude: I know that the Buoyant force on a balloon is: $F = (\rho_{air} - \rho_{helium})gV$ Using ...
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1answer
250 views

Pressure and Buoyancy [closed]

It is well known that you can trap water in a drinking straw by placing the tip of your finger over the top while the straw is in the water, and then lifting it out. The inner diameter of the straw is ...
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0answers
43 views

Definition of buoyancy

Hi I'm trying to figure out the definition of buoyancy, is this correct? So say for example I have 1 cubic meter of water which weighs 1 ton, and I placed a cubic foot of a material that at a 1 ton ...
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1answer
270 views

The Spinning Log “Perpetual Motion” problem, and my attempt at a solution

So I was introduced to this "perpetual motion" riddle a few weeks ago. The problem goes like this: we all know perpetual motion machines are not possible, but this riddle seems like it should work as ...
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3answers
1k views

Finding the density of gold crown using archimedes principle [closed]

Question: As shown in diagram below the crown has a mass of 14.7kg when measured above water and 13.4kg when measured in water. Is the crown made of gold? I have this following solution provided: ...
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6answers
9k views

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 ...
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1answer
511 views

When you breath in a helium balloon, do you lose weight?

We all know the trick of breathing in a helium balloon to get a funny squeaky voice! When you do this, would it be correct to say you lose weight? On the one hand, the helium should make you more ...
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2answers
146 views

Flying eggshells

This question was asked on Judaism.StackExchange a few days ago, but I think it has a better chance of being answered here. Disregarding the grammatical discussion in the comments on that ...
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1answer
966 views

Calculate the weight that a hot air balloon can carry [closed]

Given a hot air balloon of radius 10 meters and negligible mass, calculate the maximum weight it can carry if the density of outside air is 1.2 $\frac{kg}{m^3}$ and the density of inside air is 0.9 ...
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4answers
345 views

How does buoyancy work?

I realised, reading another Phys.SE question about balloons moving forwards in an accelerating car that I don't really understand how buoyancy works. Particularly concerning, for a SCUBA diver. The ...
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4answers
126 views

Basic buoyancy question

If I have a cup of water filled with air at the bottom of a pool, then when the cup is "upside down" the air doesn't leave because the water pressure is pushing it up against the top of the container. ...
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1answer
387 views

Terminal Velocity of buoyant object

I'm trying to figure out how much distance does a ball of balsa wood covers until reaching terminal velocity, being released from a bottom of a pool. To my understanding, I need to first figure out ...
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5answers
988 views

Is there a depth at which a human body, with lungs full of air, will no longer float?

I was watching a special on divers who dove down hundreds of feet without tanks or gear. The show referred to a depth at which the diver was no longer buoyant and would actually sink, even with lungs ...
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1answer
100 views

How does one calculate calculate buoyancy with gases?

I have hot air flowing vertically down a circular duct into the ambient cold air. I'm trying to find the power $P$ that resists the flow. I know the: Volumetric flow rate $Q$ $[m^3/s]$ Flow speed ...
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1answer
929 views

water surface tension and buoyancy

When you put a little pin on the surface of water and it floats. Is this because of surface tension or buoyancy? Can somebody also draw a force diagram for me to explain how water surface tension ...
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0answers
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Archimedes' principle: innacurate terminology? [duplicate]

All around I read that buoyancy is numerically equal to the weight of fluid displaced by a submerged object, the volume of displaced fluid being equal to that of the submerged portion (Wikipedia). ...
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2answers
509 views

Balloon, lighter than air and vacuum?

As I understand, in a balloon/air balloon, a gas burner is used to heat air or using some lighter atom like helium. Since helium or hot air is lighter and less dense than the cool air around the ...
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1answer
542 views

Upthrust vs Drag

24: A ball is falling at terminal speed in still air. The forces acting on it are upthrust, viscous drag and weight. What is the order of increasing magnitude of these 3 forces? ...
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1answer
157 views

I need to find a formula between the weight of an object and the volume of the buoy that can float it on water

So my problem is that i am working on an art instalation that needs to float. The idea is that i need to find a formula between the volume (V) of the buoy and the total weight of the whole ...
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6answers
21k views

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 ...
2
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2answers
171 views

Can a solid object float on a frictionless liquid?

Assuming the solid is less dense than the liquid, will a solid object float on a frictionless liquid? I can imagine that due to the pressure gradient the object will float, but I can also imagine ...
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2answers
135 views

Anchor of a boat

hope you can help I've been teaching my kids about pirates and when we were talking about pirate ships this morning I confused myself greatly. When carrying an anchor a pirate ship (or any vessel ...
4
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3answers
542 views

Does gravity cause Archimedes' principle and how?

Why do lighter objects float and denser sink? I understand this from the perspective that if the object can displace the equal mass of water it will float, but I wonder from the perspective of ...
2
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2answers
175 views

If the MH370 black box did sink to 15000 ft, how long would it have taken?

I have been following MH370 on the news just as everyone and latest reports seem to indicate that the black-box could be found. A recent info-graphic http://t.co/lyBBE9C2hF shows the insurmountable ...
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3answers
286 views

Question about buoyancy

I took an empty clear sphere with radius r, put some weight inside this sphere, and put in into the water. I calculate the buoyancy force as: Volume of the sphere = Volume of the water displaced ...
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1answer
149 views

Different solutions for floating a DIY torii gate deeper than it's original floating level [closed]

I'm facing a dead end with my physics experience on a new build I am working on. Any help would be appreciated. Basic problem: I am trying to build a floating wooden Torii gate to be placed on water ...
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2answers
593 views

Beryllium Vacuum Sphere Boat/Aircraft

Is it possible to make a solid rigid evacuated "balloon" out of Beryllium or other elements or alloys? The critical buckling pressure at which an evacuated sphere is given as $$ ...
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0answers
30 views

Sensor Temperature with time constant [closed]

I am having trouble with this question on my study guide. I can't seem to find anything on my previous lectures to help me out with it. It is part of my study guide and I think it will be on my exam. ...
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2answers
81 views

Stratospheric ship

Let's assume that we build a giant steel hull in a shape of cube with open top (2km long edge) and lift it to the top of stratosphere and then pump air out of it. Would it float on the outer layer of ...
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1answer
529 views

Effect of waters changing specific gravity on objects apparent weight placed in liquid

My goal is to monitor the change in specific gravity of a liquid over a period of time. My question is: What are the appropriate formula for determining expected apparent weight of an object immersed ...
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2answers
364 views

What is the third law action pair of buoyancy?

Consider a block floating in a fluid. The force due to gravity balances the buoyant force exerted on the block. But there must be a third-law action pair to the buoyant force. If the block exerts a ...
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2answers
78 views

Buoyancy of a positively charged object inside positively charged fluid

An object with a density of $x$ inside a liquid with a density greater than $x$ would float. If we assume that both of these are positively charged and the object is in the middle of the liquid: ...
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1answer
228 views

How to model a rising helium balloon?

I'm trying to model the ascent of a helium filled weather balloon from 0km to 25km altitude. The plan is to eventually use a python script to calculate the time taken to reach 25km. However, I don't ...
3
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1answer
79 views

Will a rotating body gain linear acceleration in water?

If a ball is floating in water and it has some angular velocity, will it gain some linear acceleration from the drag on it as it rotates? Edit: This is how I pictured it. I guess my reasoning is ...
0
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1answer
93 views

Can we make rigid floating helium spheres?

Is there any material that we can make rigid floating helium spheres out of without it collapsing? I have been playing with surface area and volume formulas and with a bit of trial and error have ...
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3answers
678 views

Archimedes' principle for two liquid layers

Problem: I have a cylindrical vessel of height $H$ and radius $R$. There are two liquid layers in the vessel. The first has density $D_1$ and height $h_1$, the second has density $D_2$ and height ...
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1answer
642 views

Newton's second law, gravity and buoyancy [closed]

A body of mass $m$ and volume $V$ is immersed into the sea. The body moves under the action of two forces: gravity and buoyancy (Archimedes). Gravity force has a magnitude $mg$, where $g$ is a ...
85
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8answers
16k views

Why does a helium filled ballon move forward in a car when the car is accelerating?

I noticed that when I had a helium filled, latex ballon inside of my car, it moved forward in the cabin as I accelerated forward. The faster I accelerated forward, the faster the ballon went from the ...
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1answer
472 views

How to calculate upward force of a container filled with a less dense gas than the surroundings where it is placed?

I'm trying to determine the calculation which would state the upward force of a container where the density inside the container is less then that in which it sits. Does this calculation change with ...
8
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4answers
2k views

Can air bubbles sink at extreme depths? [duplicate]

I was thinking earlier about air bubbles in water. if you had a bubble of air (say in a balloon) then as you take it down in water the bubble shrinks because of the pressure and because it is ...
2
votes
1answer
969 views

What is the buoyant and viscous force acting on a ball in free fall?

I was thinking about a situation were I have a long cylindrical jar with some viscous liquid in it. I also have a spherical ball with me. I drop the ball into the liquid inside the jar with some ...