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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Buoyant force on a certain object

Sometimes a certain body is completely immersed in water, but it does not sink deeply, it is stuck in the middle... In this case, is the buoyant force equal to the weight of the body? Why?
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1answer
56 views

Why can liquid mercury sit on salt?

A video shows liquid mercury sitting on top of table salt. Even though the mercury is much denser, it does not sink to the bottom. Why does this happen? Is the mercury just so thick that it is like ...
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39 views

Will this balloon rise?

A helium balloon contains mostly helium which is an inert gas that is less dense than the air around it, suppose I drained all the air molecules from the balloon and note that this special balloon can ...
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2answers
352 views

Why do people only float in certain orientations?

If the buoyant force on an object is equal to the weight of the water displaced by the object, why do people have an easier time floating on their back than vertically with their head sticking out of ...
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2answers
50 views

Why do corpses come back to water surfaces after sinking at first?

I want to know that why do dead bodies or corpses come back to the water surface after being sunk at first by the use of stones or anything. For what I can understand, I think it's due to water ...
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1answer
72 views

Is Archimedes' principle valid with moving objects?

I was solving a classic application of Archimedes' principle: a body partially submerged that is made to oscillate vertically and perform a simple harmonic oscillations. The equations turn out to be ...
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0answers
30 views

How is convection possible in fluids, in the absence of a contact surface for any buoyant force?

I don't understand why liquids and gases are acted upon by a buoyant force. In a solid immersed on some fluid medium, the pressure pressure difference caused by gravity exerts a force on the surface ...
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0answers
54 views

Why do clouds not fall? [duplicate]

The density difference between the clouds and the atmosphere favours the clouds to fall. Why don't they?
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1answer
73 views

Derivation of Archimedes' principle

It is my understanding that upthrust from a liquid on a body is due to pressure difference on the top of the body and the bottom of the body. How, then, is this fact used in order to derive/work out ...
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3answers
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How does potential energy work out for floating things?

Seeing a ship canal lift in TV spawned the following thought: "Oh my, this sure is a heavy ship and it can be lifted by simply adding water. What a marvellous machinery. After all, I could lift that ...
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1answer
47 views

Force Keeping Water Skier Afloat

A motionless water skier sinks because the upward buoyancy force on the skier is less than the downward force of gravity on the skier. A skier pulled by a boat does not sink into the water. Why?
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1answer
52 views

Why this is not a perpetuum mobile [duplicate]

If we imagine a device like one shown on the picture above, why can't we say that it would work? Here is a cylinder somehow placed in the fluid by one of his sides (one in the box). Due to ...
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1answer
112 views

If we dropped an object into the Pacific Ocean, would it completely sink to the bottom of the ocean floor or not?

Obviously if the density of the object is smaller than the density of water it would not sink at all. But I was thinking that, even if the density of the object is greater than the density of water, ...
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0answers
29 views

Calculating/estimating heat transfer losses for hot air balloon (lantern)

I'm trying to build a flying lantern / hot air balloon that flies as close to hovering as possible (as opposed to up-up and awaaay). To see if this is feasible I'm trying to simulate as much as I can ...
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3answers
94 views

How can Denver offer Hot Air Balloon rides?

So the air density in Denver is 1.0 kg/m^3. And heated air has the density of 0.95 kg/m^3. So adding the weight of the basket and balloon I don't understand how a hot air balloon could get off the ...
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3answers
2k views

How much do we float in atmosphere?

The atmosphere is a fluid and we have volume, therefore we displace some of it and some buoyancy force must exist. How strong is it? How much does it affect gravitational acceleration on the surface ...
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1answer
47 views

Buoyancy force on a hung object [closed]

If an object is hung with a cord and it have been embedded in a fluid, then the buoyancy force will reduce the cord tension.What is the formula that governs this reduction ?.
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4answers
230 views

Why does a metal boat float?

I was in class learning about density and stuff. Our teacher told us that things that are denser than water sink in water, and less dense things float. Then, our teacher asked us why metal boats ...
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2answers
92 views

Fundamental origin of buoyancy force?

Generally, one can think of many different forces in daily life (normal, weight, friction, EM force, buoyancy, etc.). I can think of classifying them fundamentally as in each of the 4 major ...
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1answer
29 views

Is the buoyant force on an object is the reaction force?

Is the buoyant force on an object is the reaction force for the force exerted by the objects on the fluid (newtons third law)? Or there are two sets of action reaction force? (objects force and ...
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1answer
46 views

Placing an object in a tub changes the weight of the tub?

Suppose you have a tub filled with water and it rests on a scale so you can measure the weight. If you place an object in the tub, will the reading on the scale change? Clearly if the object sinks ...
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3answers
219 views

Equilibrium using Center of Buoyancy and Gravity [Problem]

I don't understand a solution to a homework question. Specifically, I don't understand the logical sequence of each bolded statement in the answer. (b) To ensure that a ship is in stable ...
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1answer
405 views

Bowling Ball Sinking Rate - Variable or Constant?

In today's (Jan. 16, 2014) xkcd What If?, Randall Munroe discusses how fast a bowling ball will sink to the bottom of the Mariana Trench. He calculates the drag on the ball, and then plugging in the ...
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0answers
33 views

Why does a balloon filled with air weigh more than an empty balloon [duplicate]

A common experiment to demonstrate that air has weight is to weigh a deflated balloon and an inflated one. The deflated balloon gives a lower reading on the balance and hence we conclude that air has ...
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1answer
164 views

Problem regarding Archimedes Principle [closed]

A small amount of mercury is filled into massless cylindrical test tube with an even bottom and length $l=0,200m$. The test tube is put into a large swimming pool filled with water. a) How ...
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1answer
41 views

Buoyancy force in fluid dyanamics [closed]

How to calculate the force of buoyancy on a body which is placed at the bottom of the liquid container?
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33 views

Calculating buoyant force of air experimentally

I'm planning a physics project to submit at school and since it has to be something where we experimentally determine some value, previously known theoretically, I had this following idea but I want ...
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1answer
85 views

What will happen to a ball suspended in a liquid if we create air bubbles underneath it?

Suppose we have a cylinder half filled with water and a ping-pong ball, floating on the surface. We cut small holes in the bottom of the cylinder and proceed to blow air through it, resulting in air ...
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1answer
72 views

What is the motion of a balloon with a person climbing on a ladder?

Suppose you had a balloon of mass $M$ in the atmosphere at rest relative to the ground, with a ladder attached reaching towards the ground. A person (of mass less than $M$) begins climbing up the ...
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3answers
66 views

What should density of water be to keep box afloat?

I'm writing a platformer game and my physics engine is Box2D. I have successfully implemented buoyancy, but have a question about mass and density. My player is 80kg, a box has a density of 0.5 and ...
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0answers
21 views

Would a solid inside of a parcel moving due to buoyancy be affected by Bernoulli's Principle?

If a parcel (or column) of hot air were rising due to buoyancy and an extremely light solid were to be inside of this parcel (rising with it), would Bernoulli's effect cause the solid to stay inside ...
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3answers
341 views

What is the basic reason behind buoyancy?

Yesterday my friends and I were solving this easy-looking question: A metal cube is placed in an empty vessel. When water is filled in the vessel so that the cube is completely immersed in the ...
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16answers
7k views

Doesn't a box holding a vacuum weigh the same as a box full of air?

This was recently brought up, and I haven't been able to conclude a solid answer. Let's say we have two identical boxes (A and ...
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2answers
83 views

Floating objects and fluid statics

If an object is floating, I know about how buoyancy force (density of liquid* volume displaced* g) must equal gravitational force (density of object* volume of object* g). Can someone explain if it is ...
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1answer
37 views

Buoyant Force Issue

I don't understand why the buoyant force is equal to the weight of the displaced water for objects that are not "spheres of fluid." Why does the reasoning for fluid spheres hold for other objects?
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3answers
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How would filling a milk canister with helium affect the reading it makes on a scale?

Let's say that if I put a milk canister on a scale it shows 10kg. If I fill it with Helium it must necessarily be less than this, right? Can someone explain this (probably trivial) thing to me? :) ...
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0answers
67 views

Metallic coin over wooden block in glass of water

So there is some water inside a container; the height of water inside the container is $l$. I placed a wooden block on the water and it's floating to some height $x$, on top of the block is a metallic ...
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2answers
113 views

Could one make steel balloons? [duplicate]

Reading this question reminded me of an idea I once had, and I wonder whether it's feasible. Imagine a hollow ball made of something strong, like steel. Imagine there is nothing inside; only vacuum. ...
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0answers
53 views

Force if a diver is lifting a pillar out of the water?(High school physics) [closed]

A diver is searching through the remains of an old shipwreck at a depth of 45 m below the surface of the ocean. The diver finds a marble pillar that is approximately 1.7 m x 0.15 m x 0.15 m in ...
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1answer
52 views

Buoyancy Dilemma

Can you give me an example where an object (less dense than liquid) is floating in liquid and buoyancy acting on that object is more than the weight of that object ? It is impossible , isn't it? ...
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2answers
88 views

Is it a misconception? [closed]

In our textbook it is said that if buoyant force is W and weight of an object is w then object will float when W > w object will be submerged and it wont float(it will sink) when W ...
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2answers
116 views

Why won't a block less dense than water fully submerge?

Suppose we have an object of volume $1\: \mathrm{m^3}$. Mass of that object is $500\: \mathrm{kg}$, which means that the density of the object is $500\: \mathrm{kg/m^3}$. If the object is in water it ...
0
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2answers
130 views

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
140 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
897 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 ...
4
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2answers
121 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 ...
13
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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 ...
2
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1answer
165 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
104 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
131 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 ...