Buoyancy Definition and 405 Threads

Homework Statement A submarine of mass 80 000 kg is floating at rest (neutrally buoyant) at a depth of 200 m in sea water. It starts pumping out sea water from its ballast tanks at a rate of 600 litres per minute, thus affecting both its mass and the buoyancy force. Determine the vertical...

Homework Statement A hemispherical portion of radius R is removed from the bottom of a cylinder of radius R. The volume of the remaining cylinder is V and its mass is M. It is suspended by a string in a liquid of density ρ where it stays vertical. The upper surface of the cylinder is at a depth...

Homework Statement A steel pipeline carrying gas has an internal diameter of 120 cm and an external diameter of 125 cm. It is laid across the bed of a river, completely immersed in water and is anchored at intervals of 3 m along its length. Calculate the buoyancy force per meter run. Upward...

Homework Statement If a beam with square cross-section and very low density is placed in water, it will turn one pair of its long opposite faces horizontal. This orientation, however, becomes unstable as we increase its density. Find the critical density when this transition occurs. The density...

Hi all, I understand where Archimedes' Principle comes from in liquids: If we imagine a cylinder immersed in a liquid of density ρ whose cross-sectional area is A and whose top is at depth h1 and whose bottom is at depth h2: Force(top of cylinder) FT = ρgh1A Force(bottom of cylinder) FB =...

Imagine a container containing water up to 100cm of its height then I dip a cube of plastic in the water on depth of 75cm. We all know it will float because of its less density, but if we go with Pascal Law, The pressure/force applied by the water above the cube is more than than the buoyant...

I was recently tutoring a first year student, and a question of her assignment was as follows: Suppose that that you have a bucket of water over a scale. If you then partially submerge an iron rod in the water, while holding the rod so that it does not touches the bucket, will the reading on...

Hello everyone, According to Archimedes' principle, a solid body immersed in fluid (gas or liquid) always experiences a net upward buoyant force due to pressure variations occurring within he hosting fluid. Pressure calculations show that the buoyant force magnitude is equal to the magnitude...

Homework Statement A cylindrical buoy floats in sea water with its axis vertical so that it's three-fourths submerged. The buoy is 0.8m in diameter and 2m in height. Its fabricated from iron plate 10mm thick. Calculate the mass of iron chain securing the buoy. The relative density of iron is...

Hi, Just wondering if I'm going about solving this problem correctly: "A block of iron quickly sinks in water, but ships constructed of iron float. A solid cube of iron 1.6 m on each side is made into sheets. From these sheets, to make a hollow cube that will not sink, what should the minimum...

Hi, all and thanks for your time. I did read that the conservation of Buoyancy is an "alternative" conservation of energy under some hypothesis. Can someone explain how do I start from the conservation of energy and find the conservation of buoyancy? Are there some corresponding mathematical...

Hi, Really quick general question but is upthrust independent of surface area. I came across the following: "Heavy things can float on water if there is sufficient surface area to produce a big enough upthrust at a particular depth" My thinking that this is incorrect is based on the...

Homework Statement You have a hemisphere, like half a ping pong ball for example, sitting in a cup under a few centimeters of water. The hemisphere is sealed to the bottom so that no water can get underneath it. What is the buoyant force the hemisphere experiences? Homework Equations P = P0 +...

I assigned a question: Explain the physics mechanism that results in the buoyancy force. Some students replied: The floating object is interacting with the water. Therefore it exerts a downward force on the water. The water then exerts an upward force on the object due to Newton's Third Law...

I was thinking about why the buoyant force on an object should depend solely on it's volume and not shape. It seems loosely like the divergence theorem in that an integral over the surface is determined by the volume. There is a big difference though; in the divergence theorem we integrate...

As a note, this is my first post on this site. I was looking at some bouyancy calculations with regard to balloons being in air when I came across this post. I cannot understand why the calculation for the net force of bouyancy done by Vintage (the last post on the page) does not include the...

So I've noticed my little sister's helium balloons floating at the ceiling. Made me wonder if someone could create a device that could harvest energy from this buoyancy. What if I tied a very long rope to a huge balloon filled with helium, and rolled the other end of the rope to a gear attached...

Homework Statement [/B] A Raft with dimensions, 5m for length, 3m wide and 0.12m thick, is placed on water. The raft has a density of 320 kg/m^3. a) What volume of the raft is submerged into water, if the density of water is 1150 kg/m^3? b) A man and his elephant board the raft. How...

Homework Statement There is three things P, Q, R. The density of P is 2000 kg/m3, Q is 1000 kg/m3, R is 2500 kg/m3. If all of them are put into the water having density 1000 kg/m3, the correct position of the things are shown by following picture ... [PLAIN]http:// Homework Equations When ρ...

Homework Statement The first image: Without information on the interior construction of the boat or the mass distribution of the exterior shell of the boat, which of the following points can be the boat's center of gravity? The second image: Our boat from the previous question is now...

Homework Statement A 0.75-m rod has a uniform linear mass density of λ. A small mass m with negligible volume is attached to one end of the rod. The rod with the attached mass is placed in a container of unknown fluid and after oscillating briefly, comes to rest at its equilibrium position. At...

Hi there, I was just wondering if I'm thinking about buoyancy in the correct way. I understand that it is related to the water displaced and that water displaced would usually have pressure being pushed up on it by the water underneath. A boat that floats would be taking up the space of that...

1) My teacher says that the apparent weight of an object in water (floating,sunken,submerged etc) is equal to it's actual weight-buoyant force acting on it. That is, wt (ap)=wt (ac)- F(b) Where wt (ap) = apparent weight, weight (ac)= actual weight. And f (b) = buoyant force 2) But..., if an...

theres one beam of wood of density 0.5 floating on water of density one the beam is vertical and i assume it will go to horizontality this force that moved the wood beam implies a work has been done and hence potential energy has been spent but if the beam has density 0.5 it means it has the...

Homework Statement One way of moving a large undersea rock or mooring is to fasten a closed, empty oil drum to the rock while at low tide. As the tide comes in the drum is drawn down into the water increasing the buoyant foce acting on the system of the rock and drum. Suppose a cylindrical drum...

Homework Statement The rectangular gate shown in section is 3 m long (perpendicular to the paper) and is hinged about its upper edge B. The gate divides a channel leading to a fresh-water lake on the left and a salt-water tidal basin on the right. Calculate the moment, M, on the shaft of the...

Homework Statement [/B] A rectangular object has a width of 40 meters, height of 15 meters, and length of 2 meters. It floats consistently when 3 meters of its height is below the surface of the water. 1. Find the volume of the displaced water. 2. How much is the buoyant force on the object...

Hi All, I have a problem (with 3 separate instances) to which I believe I have the answers, but would like check with those more knowledgeable than myself. They revolve around 3 blocks sinking through water and which falls quicker. I am ignoring friction. Instance 1: All blocks are exactly the...

if the person sitting in the boat throws a pebble to the swimming pool. Pebble was initially contained inside the boat and of course it has higher density than water.

Homework Statement A beaker is filled with water and its weight is measured by a balance scale. The reading is recorded as R1. 1. A ping pong ball is now submerged in the water without touching the wall and the bottom of the beaker. What is the reading, R2 of the balance scale? 2. A steel...

If a hot air balloon cools enough to start descending, does it keep accelerating until it hits the ground? Assume that the air inside does not cool off anymore, and pretend that the air pressure stays the same at all altitudes. I tried testing it by dropping a coin into a pool. It didn't seem...

Hi All, So glad to have come across this amazing site and resource. I am a mature student completing an engineering degree with the Open University and I am after some guidance and help with creating a way to plot forces from a moving mechanical system. The images on the attached drawing are...

Hello, I've search for a while on these threads, and its difficult to find the answers that I'm looking for. I know perpetual energy machines are banned from topic, but closely related is the idea of free energy. Is free energy (or close to it) allowed to be a topic of conversation? Why not if...

Homework Statement 1a)How does a ball floating 50% in water move when a LARGE amount of oil is added? 1b) if something denser than water were added, how would the ball move? 1c) if the exp. was done on the moon with different gravity and no atmosphere, how would the ball move?Homework...

How does a ball floating 50% in water move when a large amount of oil is added, and why? MY Solution: I think that the ball rises because when a large amount of oil is added, the oil sinks to the bottom causing the water to be pushed up, increasing the buoyant force which causes the ball to...

Homework Statement ship arrives from the Atlantic to the Baltic sea. How much does the draft of the ship deepen due to the saltyness of the water... density of atlantic water = 1027kg/m^3 density of baltic water = 1005kg/m^3 at these depths the crosssectional area of the ship can be assumed...

Homework Statement Hi everybody! While preparing my next experiment (Kater's pendulum), I was given for homework to derive an equation to correct the buoyancy when calculating ##g##. I am given the result: ##g_c = (\frac{2 \pi}{T(\varphi_0)})^2 l_r (1 + \frac{\varphi_0^2}{8} +...

Hello :) I am an engineer and I am trying to analyse a system which basically contains a cylindrical body free-falling through a body of static water beginning with zero velocity. I am ultimately trying to find what the velocity of the object would be at a depth of 20m. In order to do this I...

In the attached picture, can I say that there is a lift force in the Y-direction, and a drag force too in the same Y-direction? FL proportional to V_fx2 ? FD proportional to V_py2 ? Is this equation of motion for the Y-direction correct here: ma = − mg − FD + V(rho)g + FL The lift force is...

If buoyancy is due to the pressure differential as we go deeper in a liquid, then that pressure differential should depend on the vertical dimension of the immersed object. Eg. if we have a long cylinder vertically placed, the pressure differential between its top surface and its bottom surface...

Hello everyone, Following Buoyancy formula, how much helium is required to help someone with 80 kg weight against gravity? While the Buoyancy depends on volume, what happens if we compress helium? Thank you in advance. Regards, Behrouz

Homework Statement A 0.02 m x 0.01 x 0.03 block of copper (density = 8.8 g/cm3) is suspended submerged in milk (density = 1.03 g.cm3) by a string. How much tension is in the string? Homework EquationsThe Attempt at a Solution My initial thought for an equation was: T+Fb(buoyancy)-mg=0 T+...

Homework Statement the buoyancy force i found id 0.751(1000)(9.81)(0.5x0.55x0.96) = 1945N , i also found that the center of gravity of submerged portion is (48/3 , 55/ 30 = (16 , 18.3) , how to find the center of buoyancy ? is the cnter of buoyancy acted half of the submerged portion , which is...

Homework Statement A ball with a mass of 250 g and a volume of 126 cm^3 is hung vertically to a spring the springs length becomes 0.690 m.Then the ball is slowly submerged in water with a density of 1000 kg /m^3 then the spring's length becomes 0.620 m. Find Buoyancy force of the water on...

Homework Statement why the floating body still stable when G ( center of gravity ) is above the B ( center of buoyancy)? Homework EquationsThe Attempt at a Solution in my opinion , the statement is worng , because when G is above B , G has the tendency to move downward , causing the object to...

Hi. Given the area, what is the shape of an infinitely thin surface that can carry maximal load on water, i.e. has the best buoyancy just before water gets in? Is it the hemisphere?

Twenty per cent (20%) of a rubber ball is floating above the surface of a pool of water. If water has a density of 1000 kg/m^3 and the ball has a mass of 3 kilograms, what is the volume of the ball?

I am curious about what it means to be neutral buoyant. If a submarine took in enough water so that it sinks down say 20 metres below the surface and stays floating at that level -- it is considered to be neutrally buoyant down at 20 meters below. If a force pulled the sub back up to 5 meters...

Homework Statement A small spherical under water ROV (remotely operated vehicle) has a radius of 0.5m and a mass of 450kg. It sinks or rises in the ocean by taking water on board or pumping it back out again. How much water must it take on board to sink at a constant velocity of 1.2m/s. The...

Hello, I have a question about buoyancy of concrete in water. If a submersible pump station is placed under water, and it has under it a concrete foundation to hold it in equilibrium. How can someone calculate the minimum weight of the concrete foundation? The pump station has a diameter: 1.6...