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2B40.10-Archimedes Principle (Buoyancy)

Watch video:

Description: This demonstration illustrates that the buoyant force on an object is equal to the weight of the water displaced.

Equipment:

  • Weights
  • Weight scale
  • Newton scale
  • Mass
  • 2 beakers, one bigger than the other
  • Glass tray
  • food coloring

Setup Procedure:

  • Pour water into the larger beaker and add food coloring. Stir using the glass rod.
  • Place the other Pyrex beaker on the weight scale and zero the scale (accounts for mass of the beaker).
  • Attach the weight too the newton scale.
  • Place the beaker full of food coloring on the glass tray

Demonstration Procedure:

  • Weigh the desired mass on the Newton scale. Record for the class. This is best done after mentioning that the scale has been zeroed too the empty beaker, so you can weigh them together and just the weight of the mass.
  • Remove the mass from the scale and attach it too the newton scale. Place the empty beaker under the spout of the larger beaker too catch any overflow of the liquid.
  • Slowly lower the mass on the newton scale into the liquid. Have the class make note of how the weight of the object changes as it makes contact with the water. Food Coloring liquid should overflow from the beaker into the glass tray.
  • Do not force the object into being totally submerged. Once the object stops becoming submerged in the liquid, record the new weight of the mass on the Newton scale. It should be lower than its weight when not in the liquid.
  • Take the smaller beaker that caught the overflow of the liquid place it on the scale.
  • Record the new weight of the mass in the water.
  • The weight of the water displaced should equal the buoyant force (the difference in weight you recorded).
  • When finished, please empty the water out into the Pyrex beakers

Example:
In our video, we used .33 kg mass of wood. The .33 kg mass of wood weighs about .33 newtons, and displaces .33 newtons newtons of water when floating. The aluminum mass weighs 9.8 newtons, but when places in the water the scale only reads 4.9 newtons. The mass of the displaced water also weighs 4.9 newtons, so the mass of water displaced is equal to the buoyant force on the mass.

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