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“Any object immersed in a fluid (gas or liquid) loses weight equal to the weight of the fluid displaced” Archimede’s Principle An object of volume 5 cm3 imersed in water loses weight equal to the weight of 5 cm3 or ml of water. Since the density of water is 1.0 g/cm3 it must lose the equivalent of 5 grams. If its initial weight is 12g then under water it must be 7 g. A liter of hydrogen has a mass of 0.80 g in a vacuum. While in air it must lose weight equal to the weight of 1 L of air which is 1.19 g. Therefore hydrogen in air has a weight of -0.39 g What is the density of a metal block of volume 8.9 cm3 that weighs 5.2 g while under water. Mass under water + mass of 8.9 cm3 water = 14.1g in air so its density in air is m/v or 16 g/cm3 We don’t bother to add the weight of the displaced air in this case. “Any object immersed in a fluid (gas or liquid) loses weight equal to the weight of the fluid displaced” Archimede’s Principle Weight immersed + weight fluid displaced = actual weight Weighing a block in air and water. Weighing a bag filled with hydrogen. The cruise ship Elation weights 110,000 tons. Which of the following can we calculate: 1. Volume of the entire ship 2. Weight of the water displaced under the waterline. 3. Density of the entire ship 4. Amount of water needed to fill the entire ship. Weight immersed + weight fluid displaced = actual weight If you weight 110 lb (50 kg) out of water and just 10 lb (4.6 kg) under water what must your body volume and body density be? 46.4 L 1.1 g/cm3 Weight immersed + weight fluid displaced = actual weight 9000 kg or 9000 L A submarine is neutrally buoyant: weightless under water. If the mass of the submarine is 300,000 kg and its total dry volume is 380,000 L, how much water must be in the tanks? Assume the density of sea water is 1.03 g/ml or Kg/L How is the submarine able to Dive? Weight immersed + weight fluid displaced = actual weight A balloon filled with Helium of volume 40,000 L whose density is 0.18 g/L at the outside temp. of 0C. The density of the air is 1.3 g/L at 0C. How much lift does the balloon supply? -44800 g or -99 lb weight in vacuum + buoyancy force = weight in air Weight immersed + weight fluid displaced = actual weight actual weight - weight fluid displaced = weight in air Eureka short cartoon explaining Buoyancy Bill Nye The Science Guy on Buoyancy A Short Quiz on Buoyancy A Puzzle Based on Buoyancy Flash Card Review of Buoyancy Flash Activity on Buoyancy Neutral Buoyancy NASA Laboratory