Q&A for How to Calculate Buoyancy

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  • Question
    What's the difference between calculating density and volume?
    Community Answer
    Calculating volume is the length x width x depth. It is expressed in cubic meters (cubic feet, etc.) since you are multiplying meter x meter x meter. Density relates the volume to the object's mass, and is calculated as mass/volume (mass divided by volume) expressed in kg/cubic meter or similar.
  • Question
    How can I tell if an object will float or sink?
    Community Answer
    If an object weighs more than an equal volume of water, it is more dense and will sink; if it weighs less than an equal volume of water, it is less dense and will float.
  • Question
    How much buoyancy does a tank measuring 6 feet by 15 feet have?
    Community Answer
    "Bouyancy" is determined by the submerged volume of the object not by the size of the tank.
  • Question
    How do I calculate pipe weight with one density inside and a different density outside if the pipe is closed?
    Community Answer
    Weight is subject to gravity and/or buoyancy. Do you mean the mass of the pipe? To find the mass of the pipe, calculate the volume of the pipe walls and multiply by the material density. Do the same for the volume of material that the pipe encloses, and add the two results together to find the mass. You can then plug this into the calculation above.
  • Question
    How do I calculate the center of buoyancy for rectangular concrete partially submerged in water?
    Community Answer
    Concrete weighs approximately 100 lbs/cu.ft while water weighs approximately 62.5 lbs/cu.ft. so the concrete has no buoyancy. Anything lighter than the specific gravity of 1 (62.5 lbs) will float. Anything heavier will sink!
  • Question
    If I know the submerged weight and buoyancy force of an object, how can I determine its weight in the air?
    Community Answer
    Buoyancy force = weight of object in water / weight of object in air. Plug in the numbers you know and solve.
  • Question
    How do I calculate buoyancy?
    Community Answer
    Buoyant force is equal to the volume of liquid multiplied by density and multiplied by the gravitational force.
  • Question
    A body floats in water with 70% of volume inside the water. When the same body floats in another liquid, it floats with 60%of volume outside the liquid. What is the relative density of liquid?
    Cabbache
    Community Answer
    The buoyancy exerted in both cases is the same because the body is at rest. If it has a volume V, then F = 0.7Vρ₁g = 0.6Vρ₂g where ρ₁ is the density of the first liquid, ρ₂ is the density of the second liquid and g is the acceleration due to gravity. The relative density is ρ₁ / ρ₂, so we need to make the densities subject. ρ₁ = F/(0.7Vg) and ρ₂ = F/(0.6Vg), so ρ₁ / ρ₂ = (F/(0.7Vg)) / (F/(0.6Vg)). F,V and g cancel out and you get ρ₁ / ρ₂ = 0.6/0.7 = 85.7%.
  • Question
    How can I find the fluid density using buoyant force and volume?
    Cabbache
    Community Answer
    Divide the buoyant force by (the volume x the acceleration due to gravity).
  • Question
    What is the buoyancy of saltwater?
    Community Answer
    Generally saltwater is hard. Hence the buoyancy of salt water will be on higher side as compared to sweet water.
  • Question
    What's the formula for sideways pressure?
    Community Answer
    Pressure is a force that acts equally in all directions. If this was not the case, then the object would move or distort as the pressure on one surface changes to balance the pressure on other parts. Calculate the down pressure and it is the same as the side pressure at that depth/height.
  • Question
    What degree should a ship be submerged in water?
    Community Answer
    It depends on the density of the water and its general wave action. Plimsol devised a safety line for this purpose. On the side of every registered cargo vessel you will see the plimsol line and the safe water level in different waters, eg WNA (winter North Atlantic).
  • Question
    What is the buoyancy of air inside an inflatable object like a pool?
    Community Answer
    The Archimedes principle states that the buoyant force is the weight of the fluid displaced. So, for a floating object on a liquid, the weight of the displaced liquid is the weight of the object. Thus, only in the special case of floating does the buoyant force acting on an object equal the object's weight.
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