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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Over-inflating weather balloons
Would it be safe to over-inflate a weather balloon if it isn't going to be used at high altitudes? I've been looking at several different balloons, but they are all measured by their burst diameter ...
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0answers
26 views
What is the ration of volume to lift helium? [closed]
I've been searching for a usable direct conversion, but most of what I've found used a lot of rounding. What is the exact formula?
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0answers
60 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 ...
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1answer
27 views
Terminal velocity and force pull [closed]
I can't figure out this problem .
Buoyancy force and gravity remain constant and viscous force by is $-kv$. And these forces all balance, but data isn't given according to that, or I am not able to ...
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1answer
48 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 ...
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1answer
37 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 ...
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1answer
85 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 ...
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3answers
151 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 ...
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1answer
62 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 ...
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1answer
47 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
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4answers
167 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 ...
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1answer
38 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 ...
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1answer
83 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 ...
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3answers
123 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 ...
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0answers
40 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 ...
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0answers
52 views
Displacement of a Rock Thrown Overboard. [duplicate]
If you have a large boulder on a boat, in a pond, and you throw the boulder overboard and into the pond, would the water level decrease, increase, or remain the same?
I believe that the level of ...
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1answer
81 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 ...
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1answer
1k 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 ...
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3answers
440 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?
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2answers
524 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
198 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 ...
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1answer
135 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 ...
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3answers
219 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, ...
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2answers
222 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 ...
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1answer
61 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 ...
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2answers
703 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 ...
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1answer
68 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 ...
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0answers
276 views
amount of hydrogen necessary to lift one pound, 200 pounds [closed]
How many cubic feet of Hydrogen does it take to lift a 1 pound object, and is the relationship between cubic feet and pounds linear, in other words would it take 200x that amount to lift 200lbs?
4
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4answers
636 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
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1answer
626 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 ...
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2answers
150 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 ...
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1answer
226 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 ...
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2answers
1k 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 ...
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2answers
708 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 ...
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1answer
408 views
Would a submarine float in the atmosphere of Jupiter?
Would a submarine float in the atmosphere of Jupiter, or would it get crushed?
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3answers
5k 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 ...
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1answer
1k 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 ...
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2answers
749 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 ...
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0answers
647 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 ...
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3answers
883 views
Counteracting g-force
Is it possible to counter-act g-force for a jet-pilot, by him putting on a scuba-diving suit
and filling the cockpit with water? On earth we are constantly pulled down, or accelerated with one g. In ...
3
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2answers
2k views
Why do helium filled balloons move away from the Earth?
From my understanding objects do not fall but are pulled to the earth from gravity.
With this in mind, I can't understand why if helium filled balloons are not pulled by gravity then shouldn't they ...
2
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2answers
1k views
Balloons and lifting gases
Hydrogen is the lightest element, so it's cable of lifting the most weight in out atmosphere (probably not the best terminology there, but you get the picture)
Would hot hydrogen (in the same sense ...
22
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3answers
1k views
What is the fallacy in this infinite motion machine?
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 ...
5
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7answers
2k views
What property of objects allow them to float?
I used to think that the shape of an object determines its ability to float (boat-shaped objects are more likely to float, and spheres tend to sink). But my friend, who is fond of making me look ...
