1. Weight of Sunken Treasure

2. Mass suspended from Spring Scale When the mass is lowered into the water, what will happen to the reading on the spring scale? A.Increase B.Decrease C.Stay the same 22 N Decreases from 22 N to 14 N, a reduction of 8 N. This is the buoyant force equal to the weight of the water displaced. 14 N This is Archimedes Principle Pressure at the bottom is larger than pressure at the top. Remarkably the Buoyant force does not depend on the shape of the immersed object! Size of a ship: she displaces so many tonnes….

3. Mass suspended from Spring Scale When the mass is lowered into the water, the spring scale reading decreases by 8 N from 22 N to 14 N. What will happen to the reading on the scale beneath the water? A.Increase B.Decrease C.Stay the same 22 N Force Plate Scale Bottom scale increases by 8 Newtons. Why? 14 N Newton’s third law: If the water exerts 8 N up on the block, then the block exerts 8 N down on the water. Need a total of 22 N to hold up the block. 14 from the spring scale 8 from the Buoyant force the water exerts on the block.

4. Vacuum 22 N If the block and spring scale were moved to a vacuum chamber, would the reading on the scale A. Increase B. Decrease C. Stay the same Reading would decrease. Archimedes principle applies to all fluids including air. But the weight of air displaced by the block is relatively small and the buoyant force is small as well.