Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and (as explained by Archimedes' principle) is equivalent to the weight of the fluid that would otherwise occupy the submerged volume of the object, i.e. the displaced fluid.
For this reason, an object whose average density is greater than that of the fluid in which it is submerged tends to sink. If the object is less dense than the liquid, the force can keep the object afloat. This can occur only in a non-inertial reference frame, which either has a gravitational field or is accelerating due to a force other than gravity defining a "downward" direction.Buoyancy also applies to fluid mixtures, and is the most common driving force of convection currents. In these cases, the mathematical modelling is altered to apply to continuua, but the principles remain the same. Examples of buoyancy driven flows include the spontaneous separation of air and water or oil and water.
The center of buoyancy of an object is the center of gravity of the displaced volume of fluid.
Hi!
I'm interested on how a 45-gallon drum (filled with air) behaves when submerged in water. I did some calculations and from what I calculated a 45-gallon drum displaces 170kg of water, therefore the upward (buoyant) force on the drum when submerged would be 170kg minus the weight of the...
Homework Statement
The density of ice is 920kg/m^3, and the density of sea water is 1030kg/m^3. What is the fraction of the total volume of an iceberg that is exposed?
given:
density sea water = 1030kg/m^3
density ice = 920kg/m^3
Homework Equations
density water/density ice...
One end of a light thin string is attached to a cork with density ρC = 0.24 g/cm3. The other end is attached to a rock. When the arrangement is placed in liquid 1 with density ρ1 = 0.80 g/cm3, a fraction f1 = 0.75 of the cork becomes submerged. When the arrangement is placed in liquid 2 with...
Good afternoon, I am having some trouble solving this basic fluids problem, and I am hoping you can look over my work, and offer some assistance.
Homework Statement
A submarine has a total mass of 2.1 multiplied by 10^6 kg, including crew and equipment. The vessel consists of two parts...
Homework Statement
A ferry boat is 4.0 m wide and 6.0 m long. When a truck pulls onto it, the boat sinks 4.00 cm in the water. What is the weight of the truck?
Homework Equations
\rho=m/v
and others
The Attempt at a Solution
none. My teacher gave my class chapter to read and...
First of all, let me just say this site is amazing idea and second of all I look forward to Contributing
A cube 6.in on a side is made of aluminum heaving Specific weight of 0.100lb/in3. If the cube is suspended on a wire with half of the volume in water and the other half in oil SG= 0.85...
A man is in a rowing boat floating on a lake, in the boat he has a brick. He throws the brick over the side of the boat so as it lands in the water. The brick sinks quickly. The question is, as a result of this does the water level in the lake go up or down?
Answer...
Homework Statement
A fisherman and his young daughter are in a boat on a small pond. Both are wearing life jackets. The daughter is holding a large floating helium filled balloon by a string. Consider each action below independently, and indicate whether the level of the water in the pond...
Homework Statement
A boat with a density of 0.75 g/cc is floating in water. What percentage of the boat is floating above the surface of the water?
Homework Equations
I don't know any general formulas for buoyancy. I was hoping someone here could provide one.
The Attempt at a...
Homework Statement
A hollow plastic sphere is held below the surface of a fresh water lake by a cord anchored to the bottom of the lake. The sphere has a volume of 0.65 m^3 and the tension in the cord is 842 N. What is the mass of the sphere, in kg? Enter your answer using 3 decimal places...
i have a physics problem about buoyancy and could really use some help!
a cubical block of wood 10cm on a side, floats at the interface between oil and water with the lower surface 2cm below the interface. the density of oil is 0.6 g/cm^3 and the density of water is 1.00g/cm^3. what is the mass...
Homework Statement
A raft is made of 11 logs lashed together. They are 38.0 cm in diameter and 6.10 m long and has a density of 700 kg/m^3. How many 60 kg persons can the raft hold in freshwater while keeping everybody's feet dry?
Homework Equations
Volume immersed/Volume total =...
A bodybuilder is holding a 20-kg steel barbell above her head. How much force would she have to exert if the barbell were lifted underwater?Fb= Density x Volume x Gravity
Density= mass/volume
7860= 20/ V
V= .00254 m^3
Fb= 1000 x .00245 x 9.81
Fb= 24.9174 N
perhaps you can help me.
on http://www.lhup.edu/~dsimanek/museum/themes/buoyant.htm fundamentally, what is the reason that the picture under the words "buoyant wheels and belts" doesn't work? (Except remove the movement of water between two buckets. replace that with compressing and...
Homework Statement
A 6cm tall cylinder floats in water with its axis perpendicular to the surface. The length of the cylinder above water is 2cm. What is the cylinders mass density?
Homework Equations
Fb-Fg = pf*vf*g = mo*g
=pf*vf*g = po*vo*g
mass density = p = m / V...
Homework Statement
In the future, astronauts living on the moon will have baths in their accommodation. When using them, will they float higher in the water than on earth? Explain fully the reasoning behind your answer.
Homework Equations
Achimedes Buoyancy
The Attempt at a...
Homework Statement
Styrofoam has a density of 300 kg/m3. What is the maximum mass that can hang without sinking from a 40-cm-diameter Styrofoam sphere in water? Assume the volume of the mass is negligible compared to that of the sphere.
Homework Equations
FB=poVog
Volume of sphere...
Homework Statement
The bottom of a steel "boat" is a 7.00 m x 8.00 m x 5.00 cm piece of steel (rho-steel=7900 kg/m^3.) The sides are made of 0.540 cm-thick steel.
What minimum height must the sides have for this boat to float in perfectly calm water
The Attempt at a Solution
I...
Homework Statement
The average density of the body of a fish is 1147.0 kg/m3. To keep from sinking, fish have an air bladder filled with air. If the density of air is 1.28 kg/m3, what percentage of a fish's body must be filled with air to be neutrally buoyant? (Note: Enter your percentage...
Homework Statement
well, this isn't really a homework question, but its a lab we're doing. the thing is that we were trying to "verify" archimede's principle but what we ended up doing is just using it. Let me explain. We took a ball and measured its mass and volume.. and found its specific...
First off, thanks in advance to anyone who can help at all. I've attempted to do a few things, and none of them seem to work...let me know what you think!
THANK YOU!
Homework Statement
A sperical bubble of radius r has a volume v and a pressure p when just below the surface of a liquid...
Homework Statement
A ball of mass m_b and volume V is lowered on a string into a fluid of density rho_f. Assume that the object would sink to the bottom if it were not supported by the string.
What is the tension T in the string when the ball is fully submerged but not touching the bottom...
Hi,
This is my first post here so please be gentle! I am looking to investigate the buoyancy force of a cuboid. The dimensions of the cuboid are 30cm x 20cm x 15 cm. When the cuboid is placed in the water (the face 30cm x 20cm faces the water), 4cm of the cuboid will be submerged. If I push the...
Homework Statement
Imagine a man in a boat holding a brick. He toss the brick in the water. What will happen to the level of the water when the brick toss in it.
Homework Equations
None
The Attempt at a Solution
I have arrived on 3 solution that's seems to be logical to me but i...
Homework Statement
A flat-bottomed barge, loaded with coal, has a mass of 2.8 x 10 ^(5) kg. The barge is 19.8 m long and 10.5 m wide. It floats in freshwater. What is the depth of the barge below the waterline?
Homework Equations
Archimedes principle
density = mass / volume
The...
Need Help Understanding a concept on Buoyancy!
Homework Statement
I have a beaker on a scale. I suspend a block on a string and place it in the beaker. Will the scale reading be higher or lower than before?
I need someone to explain the concept please
Homework Equations
The...
Hey,
The question is:
"AN object weighs 6.4 N when fully immersed in water. Find the buoyant force acting on it."
I have not even come near to the solution because it doesn't fit in the formula.
thanks in advance.
How do you find the exact buoyant force of air?
B = pgV
where p = density of air (1.29kg/m3)
g = 9.81 m/s2
V = volume displaced
The problem is, you can't measure Volume directly. You have to do it experimentally by weighing a mass in air and then in water.
I can...
I've got an interesting question about a Buoyancy problem we were given in Lab today. We were given an unknown block and we were asked to find its density without directly measuring its volume.
So we found the mass in air and in water.
Mass in air was 267.65g
Mass in water was 237.76g...
Homework Statement
How many cubic metres of helium are required to lift a balloon with a 400 kg payload to 8000 m? Assume balloon maintains constant volume, and density of the air decreases with altitude z according to the expression \rhoair = \rho^e^-z/8000, where z is in metres and po =...
question: I have a closed container filled with helium and I can't change the shape or size of the container. How can I achieve maximum buoyancy in order to make the container seem as light as possible? Would I want to jam pack the container with helium so that the pressure inside container is...
Hi All,
I'm having trouble understanding why exactly there is a net force upward when an object is submerged in a liquid. I thought the liquid exerts a force all around the object and thus cancels out...so how can there be a netforce from underneath the object?
I think my understanding...
Hi - I'm having trouble with the bouyancy force. I understand that in static equilibrium a force from below a submerged object (not resting on the floor of a container but in the liquid) equals the overlying liquid plus the weight of the object. So that the bouyancy force is the difference of...
A solid cylinder of uniform density of 0.85 g/cm3 floats in a glass of water tinted light blue by food coloring
Its circular surfaces are horizontal. What effect will the following changes, each made to the initial system, have on X, the height of the upper surface above the water? The...
the problem is:
a block that weighs W floats exactly with 1/2 of its volume below the waterline. What is the buoyant force?
Answer is W, but why is it W?
I thought that its 1/2 W because only 1/2 of the volume is below the waterline. if the buoyant force equals to the downward force...
1. Homework Statement
A 4 cm diameter cylinder floats in the water. How much work must be done to push the cylinder 10 cm deeper into the water?
2. Homework Equations
3. The Attempt at a Solution
I did the integral from 0 to .1 m of (.02m)^2 * pi * (1000kg/m^3) * (9.80) * x dx...
This question was presented as one of those "think about it" questions in my physics class. Its not worth any points, but its driving me crazy! I can't figure it out. Here it is:
Consider a pineapple sitting on a sensitive scale resting
on the bottom of a large glass jar which is connected...
Homework Statement
A 4 cm diameter cylinder floats in the water. How much work must be done to push the cylinder 10 cm deeper into the water?
Homework Equations
The Attempt at a Solution
I did the integral from 0 to .1 m of (.02m)^2 * pi * (1000kg/m^3) * (9.80) * x dx
=...
Hi,
I'm trying to achieve neutral buoyancy with a sounding balloon (a large latex balloon).
Is there a certain weight/helium ratio that will make it afloat at 10km/20km etc (tyhe balloon bursting altitude is ~38km)
One idea that I had was to attach another balloon, which is mostly empty...
Homework Statement
An iron anchor of density 7870 kg/m3 appears 290 N lighter in water than in air.
What is the volume of the anchor?
Homework Equations
Fnet = 0 (we are doing static fluids) = forces up - forces down
Fbuoyant = density of liquid*g*volume of object
density...
[SOLVED] Aluminum Boats and Buoyancy.
All right, here we go.
I'm stuck doing a "Lab Practicum" which has this specific task:
Build a boat out of aluminum foil alone. Find the maximum about of mass it can hold without tearing, capsizing, or just plain submersing into a bucket of water.
The...
Homework Statement
Derive the scaling law for static buoyancy force of a solid sphere in a liquid with a density of γ.
Assume the sphere is made of a material with a density of γs (γs< γ).
Homework Equations
The Attempt at a Solution
I calculated the the buoyancy force of the...
There is a container full of water with a hole in the bottom. The hole is sealed and fits water-tight around an enclosed cylinder (like a straw sealed at both ends). The cylinder still moves easily vertically and it is inserted in such a way that it protrudes out both the top and bottom of the...
Homework Statement
Using Archimedes' Principle and the diagram shown: (diagram is a "mass" of something in a liquid with an immersed portion (Vb) and an Un-immersed portion (Va)).
A. prove that if an object is floating in a liquid, the fraction of the object's total volume that is...
Homework Statement
An empty rubber balloon has a mass of .0120 kg. The balloon is filled with helium at a density of .181 kg/m^3. At this density the balloon is spherical with a radius of .500m. If the filled balloon is fastened to a vertical line, what is the tension in the line...
1. A solid cylinder (radius = 0.150 m, height = 0.120 m) has a mass of 6.90 kg. This cylinder is floating in water. Then oil ( = 725 kg/m3) is poured on top of the water until the situation shown in the drawing results. How much of the height of the cylinder is in the oil?
2...
Ok here goes,
A cubical box 25.00 cm on each side is immersed in a fluid. The pressure at the top surface of the box is 109.4 kPa and the pressure on the bottom surface is 112.0 kPa. What is the density of the fluid.
I know density=mass/volume and I know my teacher gave us another long...
A spherical float has a volume of 0.17 m cubed and a mass of 54kg. It is held at the bottom of a pond by a rope. The pond is filled with water. The pond is 7.6m deep. The rope breaks.
1. What is the radius of the float?
I figure that I use r=the cubde root of (3V/4pi) But I am not sure...
Homework Statement
http://img524.imageshack.us/img524/1743/buobu1.png
Homework Equations
Vsphere= pi/6(d^3)
W = mg
The Attempt at a Solution
Wc + Wo' = 0.650 N
Wc' + Wo' = 0.550 N
I'm unsure of how to do this because it asks to find the volume ONLY BY USING THE two weight...