Buoyancy and Bubbles ``` Name: Mmaryam Status: student Grade: 9-12 Country: Nigeria Date: Winter 2011-2012 ``` Question: How does the buoyancy of an object depend on the presence of bubbles? Replies: On the whole, bubbles reduce the density of water and reduce buoyancy. In fact, in teaching sailing classes we were told to warn small boat sailors about getting too close to the back of large ships and their wakes. The air bubbles in the wake close to the stern of the ship could cause real buoyancy problems! R. W. "Mr. A." Avakian The buoyancy of an object depends upon the mass of the volume of the fluid displaced. Since bubbles have a large volume per unit mass, they displace a lot of the fluid. This makes the object appear a lot lighter if bubbles are attached. Vince Calder Mmaryam An object will float if it weighs less than the water it displaces. So if I put an object in a bucket that is filled to its very top with water Then collect and weight all of the water that spills over the side of the bucket, Then if the object weighs less than the spilled water, the object will float. If the object weighs the same as the spilled water it will neither sink nor float, it will just hang there And if the object weighs more than the spilled water, it will sink. Bubbles in an object that is underwater displaces water but weighs nothing. So in that way, bubbles effect the buoyancy of an object. US Navy submarines have ballast tanks. When they want to dive, they fill the ballast tanks with water until the submarine weighs more than the water it displaces. When they want to surface they blow compressed air into the ballast tanks which expels the water from the ballast tanks and causes the submarine to weigh less than the water it displaces and the submarine floats to the top of the water. Sincere regards, Mike Stewart Click here to return to the Physics Archives

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