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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How do buoyancy control devices (BCD) work?

I get that having more air decreases density and increases buoyancy. However, we can take the diver-BCD-oxygen-tank to be a single system. How can the pumping of air from the tank into a vest around ...
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48 views

Archimedes Principle [on hold]

A block of wood floats in a beaker of water. The block experiences an upward buoyant force. If the beaker (with water and block) is weighed, would the measured weight be less than the sum of the ...
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Calculus formulas for buoyant force?

I am launching a high-altitude balloon as a part of a physics project I am working on. I know that the amount of helium I need corresponds to about 40 newtons of lift for the launch, which is all I ...
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36 views

Relation between Upthrust and Newtons Law [closed]

Using Newton's $2nd$ law of motion, show that when an object floats on the surface of water, the upthrust experienced by the object and the weight of object must be equal? The first thing is I don't ...
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Understanding Density and the Buoyant Force

A beaker of water resting on a scale registers a weight of 0.61 N. Lowering a steel cube completely into the water (without making any contact with the beaker) causes the reading on the scale to ...
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2answers
66 views

Why does the gravitational potential energy decreases as balloon filled with hydrogen ascends up?

As body ascends height increases from the formula $mgh$ the increasing height should increase magnitude of P.E. but some say we should take height negative as it is going up against gravity.
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Melting of ice in beaker [closed]

If we have (i) ice with a stone frozen and (i) ice with a wood frozen . Both of these are kept in a beaker full of water . Then what will be the the change in water level in both cases when stone has ...
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39 views

Equation of motion for ice block in water

I need to derive the equation of motion for an building block of ice that swims in water. The building block has an initial height that is looking out of the water called $h_A$ and is pushed into the ...
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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 ...
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29 views

Center of Buoyancy

Why does center of buoyancy change when a solid body is rotated along its axis of rotation? Center of mass does not change but why does center buoyancy change which further leads us to the concept ...
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19 views

hot air balloon and pv=nrt [duplicate]

[on hold] up vote-3down votefavorite A hot air balloon has a total mass 750 kg (not including the air in the balloon) and holds a volume of 2.8x10^6 L of air. Assume the density of air outside the ...
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How to keep a helium balloon between 1 to 5 meters above ground? (without it being tied)

I understand that helium balloons rise because their density is less than air, so they can rise up to a point where the air surrounding it has the same weight as the balloon. I was thinking to fill it ...
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1answer
52 views

Can u explain below diagram is possible or not [closed]

If I takes 3 balloons with same size they r connected with same thred frist end have 2 balloons and second end have 1 balloon I put same manner as shown in diagram then frist end is gos up or not or ...
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56 views

I m just try to make Free energy using buoyancy [duplicate]

Can I make power (electricity ) using buoyancy see diagram. if this diagram is possible then how much power i get . I just need formula for upwards speed.
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44 views

Is Buoyant force a reaction?

When we fall on water. The surface molecules are pushed down and as a consequence molecules below the surface molecules and molecules beneath them and so on are also pushed down. Some of them are ...
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52 views

Weighing a baloon

I know of methods of measuring the mass of a gas using chemistry, but this is unrelated. I was wondering if it is possible to deduce the mass of a helium balloon by measuring its mass it on a scale ...
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1answer
45 views

Doubt in the concept of Upthrust and Buoyancy

First of all, we know that $P = hρg$ for any depth h in a liquid. While deriving this formula we use (mg + P1A) - P2A = 0, where P1 and P2 are pressures on the upper and lower surfaces respectively. ...
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2answers
122 views

Why do helium balloons rise and fall?

I understand why a regular party balloon filled with helium falls over time due to leakage of the helium. However I've also noticed that recently filled helium balloons put outside rise and fall. At ...
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1answer
100 views

Physics:Buoyant force and scale readings

Sorry this might seem like a dumb question, but I'm having trouble understanding the concept behind buoyant force and scale readings. Suppose I have a beaker filled with water, and the beaker is ...
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2answers
118 views

Why buoyancy is applied on centroid?

My book says: "The point of application of the buoyancy force is the geometric center(centroid) of the submerged part of the body, whereas the specific gravity of the fluid is constant." But why ...
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1answer
75 views

Permanent flying balloon

We all know balloons which are filled with gas that's less dense than air. After a few hours, the balloon drops to the ground. The reason for this phenomenon, as far as i understand, is that the ...
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1answer
84 views

Why does the water level go down when a dense object is moved from a boat to the bottom of the pool [duplicate]

Imagine you have a container ship with an extremely heavy mass on it. Why does the water level on the ship drop when the mass is placed in water?
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Is the reason why water in a cup rises if a solid is placed within it the ideal gas law?

Let's say you have a cylinder with water that takes up volume V and has temperature T. When a solid mass is placed within the cylinder, the water momentarily takes up a smaller volume within the ...
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50 views

A pure water ice cube with sides 2cm long floats in a liquid in a glass beaker [duplicate]

A pure water ice cube with sides $2\,\mathrm{cm}$ long floats in a liquid in a glass beaker. What volume will be below the liquid surface if the liquid is a) pure water and b) brine? ...
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75 views

Would the level of the water be rising, falling, or staying the same? [duplicate]

one day you were standing on the shore of a small lake. you looked out onto the water and saw a boat. in the boat were two men with five huge steel beams. the men were sidling the beams out of the ...
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How come a cork float to the side of a glass? [duplicate]

There's a not-so-recent video by a user named quirkology here, where he shows bets that usually work. From @2:19, he puts a wine bottle cap at the center of a glass ...
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31 views

How to calculate the depth of a flow meter so that there are no air bubbles in the stream

A mix of air and water (foam) is flowing into a tank from the left and going out to the right. To the right there is a suction pump. The tank is divided by a middle vertical wall that stretches from ...
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61 views

Making sense of the Buoyancy force [duplicate]

I was reading about how to find the buoyancy force when I came across this explanation: Imagine a box submerged in a tank of liquid. The distance from the surface of the liquid to the bottom ...
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1answer
61 views

If the surface tension is reduced to half(say by using a surfactant), what would be the effect on the size of an air bubble in the liquid

If I reduce the surface tension to half of the original value, what would be the effect on the size of an air bubble in the fluid? What would be the effect on buoyancy and drag forces? Also, if I ...
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1answer
76 views

Where Does the Energy Come From in this Example?

I can't figure out where the energy comes from for the work in a video I found about how the pyramids could have been made. (I do not have enough rep to post the link of it as well as the picture but ...
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2answers
143 views

Density of a substance [closed]

I have faced a question related to Archimides' principle which is all about a car sunk in water. They said calculate the average density of the car, but i really don't what does an average density ...
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1answer
97 views

Levitating capacitor

As the title already says, I would like to make a large capacitor levitate. Before you dismiss this question please hear me out: In essence, this is intended to be a way to avoid the constrains of a ...
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62 views

Does buoyancy change on smaller scales?

For baseball size objects on the order of centimeters across we have experience with what floats and what doesn't. A stick will float and a rock will not. But what if the rock were a grain of sand? ...
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254 views

Why do I sink then float in a swimming pool?

Was swimming this morning and observed something strange: if I stop treading water, hold my legs together, arms pressed against my sides, then I sink to about 3m below the surface, and then rise again ...
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1answer
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Could a vacuum airship be possible? [duplicate]

According to Wikipedia, a vacuum airship is a hypothetical airship that is evacuated instead of using a lighter gas. Really, once I first saw this, I thought, "Why did I never think about this ...
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3answers
108 views

Pull-ups in water

I realized a couple days ago that I honestly did not learn in school why it is easier to do pull-ups in water than out of it. The only answers that I found are "because you're in water so there is ...
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2answers
109 views

Is it possible to reach outer space with this method? [duplicate]

Could we use a hot air balloon to carry a rocket and send it into orbit at a higher altitude? That is, do I need to reach a specific speed to be completely free of Earth's gravity, or can I just ...
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4answers
101 views

Is it possible to make a low dense object sink in a fluid of higher density by cutting the object in particular shapes?

As we know that pressure becomes greater with decrease of height in a liquid column. If an object having lower density than that of the liquid cut in a shape of a pyramid or a right circular cone is ...
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3answers
618 views

How many grams of helium are required to lift an object weighing $X$ grams?

I once saw a video on youtube about how a man used a collection of balloons to lift himself along with his lawn chair from one side of Los Angeles to the other. My understanding of physics is a bit ...
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45 views

Pool full of Jell-O

Imagine I have filled my backyard swimming pool (8 feet deep) with a solid block of Jell-O. What would happen if I tried to swim in it? My understanding is that the viscosity of the "water" doesn't ...
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1answer
83 views

Balloon aerodynamics

In this recent anime that I have seen, there is a part where an atomic bomb is sent to the stratosphere in a box, by a helium balloon. As you can see in this picture of the set-up, there is a tube ...
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1answer
571 views

Why is the force acting down on an object submerged in a fluid only equal to the force of gravity?

I was reading through a solution to the following problem: What acceleration will a completely submerged object experience if its density is three times that of the fluid in which it is submerged? ...
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1answer
129 views

Helium balloon stays on the floor

So yesterday I came back home with a buoyant helium balloon (no comment, and before you ask, it's blue) and I left it in the house. Obviously, it rose to the ceiling. This morning I woke up to a ...
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119 views
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42 views

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
652 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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1answer
47 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
566 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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96 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
192 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 ...