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.
Homework Statement
A rectangular bar of soap floats with 3.5 cm extending below the water surface and 1.5 cm above. what is its density?
Homework Equations
p(rho)=m/v
The Attempt at a Solution
I don't know how to compute the volume since we are given only two lengths.
Athough...
Homework Statement
A thin wooden plank 1m long is kept on the protruding stone with some of its part immersed in water.
Will the centre of gravity of the wooden plank be inside the water or outside?Homework Equations
The Attempt at a Solution
For the wooden plank to be in equilibrium, moments...
Suppose you had a hollow tube, closed at both ends. The tube weighs 10 pounds and would float in water.
Suppose also there is an empty container with a hole at the bottom. The tube is stuck through the hole so that half of it is in the tank and half is sticking out the bottom. Assume a...
(volume of body)=(0,1metres)^3
(weight of body outside the barrel)=10
(weight of barrel with water without the body)=20
(weight of barrel with water and the body at the bottom)=20+10=30
Where's buoyancy? If there is buoyancy in this case, shouldn't the weight of the body inside the barrel be...
If a cube submerged in water is attached to the floor with a telescopic cylinder taking up part of the surface area on the bottom of the cube, will the buoyant upward force be a fraction of the surface area on the bottom of the cube exposed to water, or will the full buoyancy effect take place...
Ballon with density 1,2kgr/m^3 (including its cover, thus it contains a gas lighter than air), of a volume of 1m^3, placed in water.
Taking in account buoyancy, but ignoring water resistance, what is the acceleration with which it would move upwards?
Hi,
I am having a doubt with centre of buoyancy. I referred some books but still the doubt is not clarified.
Centre of buoyancy is the point where the mass of displaced water acts upon (upwards). When a steel part is completely immersed in sea water, the shape and volume of water displaced...
1. Homework Statement
A 700 g solid cube of edge length 10 cm floats in water. If the density of water is 10^3 kg/m^3, find the volume of the cube outside water.
2. Homework Equations
So the solution to this tells me that 'the weight of the cube should be balanced by the force of...
Let's say we have a solid cylinder which is fully submerged in water or any fluid having density lower than of cylinder's density. I want to find out how can we convert the buoyancy force in terms of pressure. Actually I am doing FE analysis of this kind of problem and software allows to apply...
Homework Statement
A raft is made of 11 logs lashed together. Each is 35 cm in diameter and has a length of 5.6 m. How many people can the raft hold before they start getting their feet wet, assuming the average person has a mass of 70 kg? Do not neglect the weight of the logs. Assume the...
Homework Statement
A helium meteorological balloon is made of a bag of impervious fabric that does not stretch, and when fully inflated forms a spherical shell of 1m diameter enclosing the He. At launch it is filled with He (at STP) to 15% capacity. The launch takes place in the Antarctic, in...
You're floating in a boat in a pool with a 100 pound rock in the boat.
You carefully measure the water level of the pool.
Then you toss the rock out of the boat into the water. It sinks to the bottom.
Does the water level of the pool go up, down or stay the same?
Quantitative...
A number of questions have come up on canoe forums relating to the “buoyancy” of different woods out of which paddles can be made. The general issue has been to make the most “buoyant” paddle.
Generally, here’s the goal. In certain canoe strokes called in-water slice returns, you don’t lift...
Hi all,
In the attached image I have a cylinder shaped wheel with a air pocket embedded near its edge. The wheel has the same density as water and is fully submerged in a tank of water. Also the wheel is only free to spin about its center axis. If the wheel is rotated down the air pocket will...
Hi i have this question:
A balloon is filled with helium gas which weighs approximately one-seventh of what air weighs under identical conditions. The balloon has a diameter of 10 m and carries two people, each weighing 70 kg. Assume the density of air is 1.16 kg/m3 and neglect the weight of...
I have a question which relates to buoyancy and swimming.
One of the basic skills required to be a good swimmer is to be able to maintain a horizontal postion throughout the length of your body whilst swimming front crawl but to rotate your whole body about a horizontal axis which passes...
Homework Statement
The 3m plank shown in section has a density of 800 kg/m3 and is hinged about a horizontal axis though its upper edge O. Calculate the angle theta assumed by the plank with the horizontal for the level of fresh water shown.
Homework Equations
Whats wrong with the editor...
Hello everyone,
I'm bit confused about buoyancy. First of all I want to know if it is Newton's third law, filling a vacuum or none of above. For example these are my 3 diffferent understandings of what buoyancy could be. Which one is right
I fall on water and diplace water molecules, do...
another buoyancy problem. help!
Homework Statement
The density of water is 1000 kg/m3. A block of wood of uniform density floats so that exactly 3/4 of its volume is underwater. What is the density of the block?
Homework Equations
b=mg
p=m/v
The Attempt at a Solution
not sure...
Homework Statement
A 2.5 kg block of wood is floating in water. What is the magnitude of the buoyant force acting on the block?
Homework Equations
The Attempt at a Solution
m=2.5kg
b=mg=2.5*9.81
b= 24.5N
Is this right? Thanks in advance for the help!
Homework Statement
1. You put a tomato into a vessel of salty water - it floats. Now you pour olive oil into the same vessel. Which one of the following statements is true?
a. More of the tomato will be above the surface of the water.
b. The tomato will stay at the same height.
c. Less of...
Question
Suppose that you release a small ball from rest at a depth of 0.610 m below the surface in a pool of water. If the density of the ball is 0.290 that of water and if the drag force on the ball from the water is negligible, how high above the water surface will the ball shoot as it...
Hi people.
Please explain me, why in a horisontal pipe (closed) a bubble go to middle, and not stay in any other position?
Also what is the difference of forces when this bubble moves from right/left to middle and when it rise from bottom to top.
I know bubble rise due to buoyancy...
Hello guys,
I've been toying with some ideas in my head about a project I'm working on. I want to make sure I'm doing this right. FYI, I'm not a physicist but a business major with a knack for science/math.
Is it possible to 'inject' a buoyant object into a body of water from under the...
Hi all,
If i attach a cylinder at the bottom of the water tank such that some of its part is out out of water. So in this case what would be the buoyancy force acting on the cylinder?
-agtee.
Homework Statement
"friend with a mass of 79 kg ponders the idea of attaching a helium-filled balloon to himself to effectively reduce his weight by 21% when he climbs. He wonders what the approximate size of such a balloon would be"
solution is expressed as cubic meters
apology if this entry...
Homework Statement
A small boat is floating in a swimming pool. The boat contains a heavy rock. If the rock is tossed out of the boat into the pool and the rock sinks, what happens to the water level in the pool? What if the rock floats? What if the rock became submerged in water (but didn't...
Homework Statement
I've been working as part of a study group, but I doubt that the result we reached in class is correct, so would someone check our work?
The problem statement: A cargoship weighs in at 115578 ton and lies still in the ocean. The density of the saltwater is given at 1030...
A crane lifts the 18,000kg steel hull of a ship out of the water.
The density of steel is known to be 7.8 x 103 kg/m3, while that of water is 1000 kg/m3.
A) While the steel hull is fully submerged in the water, what is the volume of water displaced by the hull? I really have no idea how to...
Hi,
A cylindrical log with volume 2.0m^3, length 4.0m and density 700 kg/m^3 is anchored to the sea floor by a light cable attached to one end, and with the long axis vertical. Density of sea water is 1030 kg/m^3. g=9.80 m/s^2.
a) What is the buoyancy force acting on the wood?
I did...
Homework Statement
Because gasoline is less dense than water, drums containing gasoline will float in water. Suppose a 260 L steel drum is completely full of gasoline.
What total volume of steel can be used in making the drum if the gasoline-filled drum is to float in fresh water...
Homework Statement
An empty rubber balloon has a mass of 0.0122 kg. The balloon is filled with helium at a density of 0.179 kg/m3. At this density the balloon has a radius of 0.467 m. The acceleration of gravity is 9.8m/s2. If the filled balloon is fastened to a vertical line, what is the...
Homework Statement
A helium filled balloon is tied to a 2.00-m-long, 0.050 0-kg uniform string. The balloon is spherical with a radius of 0.400 m. When released, it lifts a length h of string and then remains in equilibrium as shown in figure P14.51. Determine the value of h. The envelope of...
Is there a difference in submerged objects and floating objects? I know in floating objects that the Force of Buoyancy has to equal the Force of the object, but I'm not sure about submerged objects. What exactly is a submerged object?
Another question I have: what exactly does volume have...
Homework Statement
A flotation device is in the shape of a right cylinder, with a height of 0.500 m and a face area of 4.00 m2 on top and bottom, and its density is 0.400 times that of fresh water. It is initially held fully submerged in fresh water, with its top face at the water surface...
Homework Statement
With the nose above the water, about 95% of the body is submerged. Calculate the power expended by a 50-kg woman treading water in this position. Assume that the average density of the human body is about the same as water (p = pw = 1 g/cm3 ) and that the area A of the limbs...
Homework Statement
1. A block is 7 cm wide, 8 cm long, and 2 cm tall and has a mass of 67 g.
a) What is its volume?
b) What is its density?
c) Floating in water (with the 7x8 face down), how deep will the bottom be (what is x in
figure 2)?
d) How much extra weight can it support without...
Homework Statement
In the laboratory, you are given a cylindrical beaker containing a fluid and you are asked to determine the density \rho of the fluid. You are to use a spring of negligible mass and unknown spring constant k attached to a stand. An irregularly shaped object of known mass m...
Ok, so I've a couple of assignments that require the understanding of the basic principles of buoyancy and displacement of a ship and I'm a bit confused.
Consider a ship that has a displacement of 7 000 000 kg. That's the mass of the water that the ships displacement "pushes out" from its...
So, it looks like I'm not likely to get an answer to the https://www.physicsforums.com/showthread.php?t=345179", but I figured whilst I was here I'd ask something that's had me curious for years.
Buoyancy causes things to float/fly when the average density of a body is less than that of the...
Homework Statement
Calculate the balloon lift if it were submerged in water.
Volume of balloon (sphere) = \frac{(5^3)*(pi)}{6} = 125pi/6
The balloon is filled with hellium.
Pfluid (water) = 64.2 lb/ft^3
Homework Equations
Lift = Volume * gravity * (Pfluid - Pbody)
\frac{Pfluid}{Pbody} =...
Hello,
I'm new here, and have a confession: I'm not a physicist, merely a games programmer. Please be gentle with me, and speak slowly :smile: The stuff I'm looking into seems to be outside the scope of all of the games programming forums I know of, so I thought I'd try here.
I'm working...
My robotic team and I are constructing an underwater autonomous vehicle. We are trying to do as much of the design process in Pro-E as possible to make life easier for us down the road. One aspect of testing which would be made much easier is buoyancy testing. Therefore, I was wondering if it...
Homework Statement
A 0.900 g balloon is filled with helium gas until it becomes a 25.0 cm-diameter sphere.
What maximum mass can be tied to the balloon (with a massless string) without the balloon sinking to the floor?Homework Equations
Fb=VSphere*Pair*Gravity
Fg=Vsphere*Phelium*Gravity
The...
Homework Statement
" A spherical balloon has a radius of 7.35 m and is filled with helium. How large a cargo can it lift, assuming that the skin and structure of the balloon have a mass of 930 kg? Neglect the buoyant force on the cargo volume itself."
Homework Equations
So F(b) = (mass...
Can someone give me a formula or give an approximate approach to calculating the time it would take for an object to be raised up (due to buoyancy) from a certain depth of water?
For instance, take a ship (say it weighs 300,000kg and it's a rectangular shape with surface area of 100m square...
so with buoyancy and liquid pressure i am pretty sure i know the answer but i just want to confirm (please don't laugh if it's obvious)
- upwards buoyancy pressure only acts on the surface of a structure that is faced down
- the bottom of the structure that supports all the mass of the...
Homework Statement
A beaker with water is in equilibrium with a certain weight in a balance. Then we tie a cord to a stone, and soak the stone in water, without touching the bottom. What will the balance read and why?
http://dl.getdropbox.com/u/698994/ilustra%20forums/experiencia%20empuxo.png...
I guess it makes sense that the buoyant force of an object is equal to the weight of the displaced fluid, but why should this be the case? Why should that displaced liquid provide an upward force on the object?
It seems apparent that as long as there is some part of the object above the...
Homework Statement
A chunk of carbon steel with density, ρ = 7.84 g/cm3 , is completely submerged in fresh water. The chuck of steel weighs 30 N more in air than in waterHomework Equations Fb= ρgV ?
The Attempt at a Solution How do you find the buoyancy without being given the volume? Should I...