Tagged Questions

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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80
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8answers
11k 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 ...
1
vote
1answer
272 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 ...
7
votes
4answers
1k 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
569 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 ...
4
votes
3answers
1k views

Buoyancy of compressed air

In the movie Transporter 3 a submerged car is floated to the surface by filling a large bag with air from the tyres. I know that movies are about the worst places to get examples of physics in ...
4
votes
1answer
419 views

Plastic bottle floating and sinking

I was doing this experiment: i take a plastic cup, put in a container of water, it floats – then when I put a coin in the water, it sinks and rests at the bottom. So to make the cup sink, i fill it ...
0
votes
1answer
297 views

Can the buoyant force on an object be seen as reduction in weight on a scale?

Consider a container with some fluid of density $\rho_l$ and volume $V_l$. This is kept on a measuring device and has weight $\rho_l V_lg$. Now, consider a block of density $\rho_b$ and volume $V_b$. ...
1
vote
1answer
1k views

Definition of Buoyancy Flux

I've seen in some papers the definition of buoyancy flux as follows $$B = g \frac{\rho_a-\rho_0}{\rho_0}Q$$ where $g$ is the gravity acceleration, $\rho_a$ is the density of the ambient fluid, ...
2
votes
1answer
164 views

Buoyancy in muddy water

Consider the buoyancy force in water with very small but macroscopic particles in it. Such particles (suspension) will very slowly drift downwards and will eventually settle on the bottom. If one did ...
2
votes
1answer
125 views

Time to immerse in a fluid

Whenever you drop an object in water, it takes some time to get fully immersed. I was wondering if this depends upon the buoyant force of the water on the object, slowing it down. However, I was not ...
-1
votes
1answer
100 views

Are the forces I'm using correct? (ball in air) [closed]

I have been working on a program which should simulate all the forces on a spherical object. Right now those are balls, but they can easily be changed to something else. These are the formulas I use ...
1
vote
2answers
226 views

Help with buoyant forces and liquids (high school physics)

I am stuck on this problem. Here is the scenario Suppose you send a balloon (filled with air) from your submersible craft to the surface of the ocean, $10.8 \text{ km}$ above, with the ...
1
vote
1answer
348 views

Buoyancy Problem - Cubes in water

I have a tank with water (10 m high) , with an ideal seal at the bottom (water can't fall down, but can enter bodies). I have a system of 6 cubes ( of polystyrene density= 20 Kg/m^3) with dimension ...
-7
votes
2answers
208 views

What is the sensation by man carrying a water bucker with an object floating in it? [closed]

A man is carrying a bucket with water. If a object is kept in it which floats in water, man will feel 1) heavier 2) lighter 3) none I think when the body floats its weight is balanced by upthrust ...
-1
votes
1answer
126 views

Lifting house with balloons [closed]

I have an assignment about the movie Up. Here is the question: Critique the brief floating scene. Did the animators use enough balloons during this scene? What important variables, (which affect ...
1
vote
1answer
3k views

Floating Objects and Weight

The Situation: A ball is placed in a beaker filled with water and floats. It is also attached to the bottom of the beaker via a string. The Question: The ball is attached to the beaker, thus ...
0
votes
1answer
118 views

Finding the work required to move an object under pressure without knowing volume

"What is the least amount work you must issue onto a silver ingot with a mass of 38 kg at 26 meters depth to bring it to the surface?" I'm not sure how to do this one. Surely it depends on the volume ...
4
votes
1answer
959 views

Application of Archimedes Principle

A candle is floating in a liquid placed in a container. The container is a cylinder of diameter $D$, and the candle is of width $d$. ($D>d$) The height of the liquid from the bottom of the ...
0
votes
3answers
6k views

how dense fluid affect the buoyancy force?

I read a story regarding the Archimedes' principle in a magazine of popular science and I am thinking of the following question: how does the density of the fluid change the buoyancy force for the ...
2
votes
1answer
391 views

How does the buoyant force on a cube at the bottom of a tank of water manifest itself?

Let's say a 10N cube (in air, on Earth) rests flat on a scale at the bottom of a tank of water, and the scale reads 8N, so there is 2N of buoyant force on the cube. How does the buoyant force ...
1
vote
1answer
115 views

Measure density with the help of buoyancy

I am trying to derive a formula to calculate the density of a irregulary shaped object. I can measure the (false) weight of the object in pure air (of known density), and the (false) weight of the ...
5
votes
4answers
339 views

Can a balloon be used as an anchor point for a pulley?

For a physics/ engineering contest, I want to use a large balloon as an anchor point for a pulley. This would allow me to raise and drop masses. However, in testing, when I pull on the pulley the ...
0
votes
1answer
255 views

When moving something by entrainment in a fluid stream, where does the energy come from?

The particular Something I had in mind here would be air bubbles that are pulled downwards against their buoyancy by a stream of water falling down a shaft. The work required to push those bubbles ...
6
votes
1answer
268 views

In a column of rising hot air, is the velocity higher at the top?

Since the movement of the air is induced by buoyancy, i. e. there's a constant force acting on the air, so I would expect the velocity to increase during ascent, much like an object falling down due ...
3
votes
3answers
613 views

How do I correctly express the work required to put an object with positive buoyancy down into a certain depth (of water)?

It seems to me that I can express the work required to put an object under water in the same way that I express lifting an object up against gravity. I. e., in both cases I increase the potential ...
1
vote
0answers
154 views

How do I calculate the energy balance of a trompe?

I was quite fascinated by the concept of an ancient type of air compressor, called a trompe. It entrains air bubbles into a falling stream of water via the Venturi effect, and extracts the air at a ...
0
votes
0answers
61 views

Displacement of a Rock Thrown Overboard [duplicate]

Possible Duplicate: Basic buoyancy question: Man in a boat with a stone If you have a large boulder on a boat, in a pond, and you throw the boulder overboard and into the pond, would the ...
1
vote
1answer
166 views

How do I correctly scale down a space capsule for testing its physical behaviour on splashdown?

Kristian von Bengtson (on twitter, on Wikipedia) of Copenhagen Suborbitals is building a downscaled test item to test the design for their space capsule. He notes that as volume and area scale down ...
5
votes
3answers
3k views

How much lift does the average latex helium filled party balloon produce?

How much lift does the average helium filled party balloon produce? (not including any extras like ribbon string)
2
votes
1answer
3k views

Boussinesq approximation for the Navier Stokes' equation - discrepancy

In the Navier Stokes' equation: $\rho_0 \left( \frac{\partial v}{\partial t} + v \cdot \nabla v\right) = -\nabla p + \mu \nabla^2 v + \hat{f}$ I included the temperature variation of density as ...
3
votes
3answers
2k views

Cause of buoyant force?

Can you explain to me what causes the buoyant force? Is this a result of a density gradient, or is it like a normal force with solid objects?
2
votes
3answers
3k views

Dropping an anchor from a boat

A yacht on a lake drops its anchor overboard. What happens to the water level in the lake? It rises very slightly. It falls very slightly. It stays exactly the same. It's impossible ...
5
votes
2answers
652 views

A man on a boat, with something in his hand [duplicate]

Possible Duplicate: Basic buoyancy question: Man in a boat with a stone A man is on a boat, in the middle of a quiet lake. He has something in his hands (anything you like) He throws the ...
0
votes
1answer
338 views

Calculate the stable height of a balloon

My son has asked me a question, and I'm afraid my high school maths are not up to the task: Is it possible to calculate the height that a given balloon (filled with a known quantity of helium) will ...
2
votes
3answers
881 views

Buoyancy in gases

If buoyancy is caused by pressure gradient and if the pressure of a gas is same everywhere in its container, which means there's no difference of pressures on surfaces of the lighter-than-air object, ...
-2
votes
2answers
328 views

Infinite Energy from Bobbing

Could this device theoretically continue in motion forever? If not, why not? (click below for images): Device description. Device process. The device is less dense than air, so it rises. The ...
0
votes
1answer
101 views

In hydrostatics, is it possible for the bouancy to be greater than the weight of a body?

In the diagram we have two bodies, with density and volume $\delta$ and $V$, and a fluid $\ell$. $$\delta_1=0,7 \rm\frac{gr}{cm^3}$$ $$\delta_2=2 \rm\frac{gr}{cm^3}$$ $$V_1=100 \rm {cm^3}$$ $$V_2=10 ...
3
votes
2answers
6k views

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 ...
1
vote
1answer
92 views

How do we describe the relationship of balloon size and related lift?

We know that hydrogen and helium are lighter that air. Therefore it is certain that they would create a lifting force when enclosed in a balloon. How do we describe the relationship of balloon size ...
5
votes
4answers
1k views

Costa Concordia shipwreck: why can't they right the ship with pingpong balls?

So I guess I don't really understand the situation in question... I heard a radio piece about the Costa Concordia shipwreck in Italy taking 7-10 months to remove the vessel from its place of resting, ...
6
votes
1answer
3k views

How does placing objects in liquids affect the mass?

I was dazing off in my physics class when I came up with this question and I was wondering about it all day. I could not provide myself with an adequate solution, so here I am asking the forum about ...
1
vote
2answers
176 views

Does a Lorentz-contracted object float or sink?

Consider the following thought experiment: Imagine an object of a certain mass density which allows it to float in water. Now if this object is viewed from a moving frame with high speed, it will ...
2
votes
1answer
397 views

Buoyancy experiment with my child

I've read through a few other answers here on buoyancy and I was hoping to get some guidance on discussing it with at 5th grader. So, taking a ball of playdoh clay and dropping it into a container of ...
1
vote
2answers
10k views

Why does density decide whether something floats or sinks? [duplicate]

Possible Duplicate: Balloons and lifting gases I understand that density of an object dictates whether or not it will float, but what I don't get and can't get any satisfactory ...
0
votes
2answers
3k views

Why does an object when filled with water sink, but without water inside float (in a body of water)?

Why does an object sink when filled with water, even if the same object would float without water inside? For example, put an empty glass cup into water, and it floats. But if you put a plastic ...
13
votes
1answer
714 views

Would a submarine float in the atmosphere of Jupiter?

Would a submarine float in the atmosphere of Jupiter, or would it get crushed?
3
votes
3answers
14k views

Buoyancy: helium vs hydrogen balloons

Given I have two identical balloons on earth, how will the buoyancy compare between the one filled with helium and another filled with hydrogen? How can I calculate the ratio of buoyancy given two ...
2
votes
1answer
3k views

“Troll physics”: Buoyancy for infinite power [duplicate]

Possible Duplicate: What is the fallacy in this infinite motion machine? Most of the "troll physics" images I can figure out, but this one has me stumped. What is broken about the following ...
9
votes
2answers
1k views

The Galileo thermometer: why do the bubbles float in the middle of the tube?

If the water were uniform temperature, it would have uniform density, so a bubble should either be all the way at the top (if it's lighter than water) or all the way at the bottom (if heavier). But in ...
2
votes
0answers
1k views

Measuring the spring constant in a system with hydrostatic buoyancy

I have a physics lab tomorrow and I would appreciate it if you could give me your opinion on whether my reasoning is correct for this situation or not: http://i.stack.imgur.com/WMzA7.jpg The title ...