2What is Buoyancy ?Buoyancy is the upwards force that fluids (liquids and gases) exert on objects which are immersed in them.We shall use the term ‘buoyancy force’ but the term ‘upthrust’ is commonly used as well.
3Floating and SinkingWhen an object is surrounded by a fluid, it will float if the buoyancy force is bigger than its weight.buoyancy forceobjectweightIf the weight is bigger than the buoyancy force, the object will sink.
4What causes the buoyancy force ? Pressure increases with depth in a fluid.So the pressure on the bottom of an object immersed in a fluid is greater than the pressure on the top of the object.This means that the force pushing up on the bottom of the object is greater than the force pushing down on the top of the object.The extra upwards force is the buoyancy force.
5Buoyancy in pictures Pressure increases with depth Low pressure at top Pressure at the sides cancels because it is equal and opposite at all depthsHigher pressure at bottom
6Buoyancy in picturesPressures cause a force down on the top and a force up on the bottomLow pressure at topHigher pressure at bottom
7Buoyancy in picturesPressures cause a force down on the top and a force up on the bottomSmall force down on topBigger force up on bottom
8Buoyancy in picturesTop forceBottomforceBuoyancy force