# 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.

130 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?
105 views

### 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 ...
77 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? ...
90 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 ...
550 views

### 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 ...
34 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 ...
69 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 ...
108 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 ...
124 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 ...
235 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 ...
161 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 ...
77 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? ...
369 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 ...
1k views

### 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 before?!...
156 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 ...
131 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 ...
118 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 ...
1k 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 ...
46 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 ...
119 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 ...
771 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? ...
191 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 ...
189 views

### Infinite energy with water and air balls [duplicate]

Question: Why wouldn't this work?
55 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?
970 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 ...
51 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 ...
752 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 ...
105 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 ...
225 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 ...
52 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 ...
59 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?
1k 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 ...
322 views

### 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 ...
218 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?
144 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 additional ...
434 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, ...
128 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 ...
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 ...
90 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 ?.
3k 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 ...
284 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 forces/...
56 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 ...
248 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 ...
2k 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 ...
602 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 ...
37 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 ...
237 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 much ...
130 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?