3Buoyancy in a LiquidThe downward weight of an object (force due to gravity) is not as great as an upward force on that object called the buoyant force or buoyancyWeight
4Buoyancy in a LiquidThe force of pressure is greater at the bottom of the object than the force of pressure exerted on the top of the object.
5Therefore, the buoyant force is due to the pressure differences between the top and the bottom of object.
6Buoyancy arises from the fact that: fluid pressure increases with depththe increased pressure is exerted in all directionsthere is an unbalanced upward force on the bottom of a submerged object
7Buoyant Force Equals Weight of Liquid Displaced any object placed in water displaces a certain amount of waterthink about how the water level in the bathtub rises when you get inyou can use the weight of the displaced water to determine the buoyant force
8Buoyant Force Equals Weight of Liquid Displaced What is the buoyant force on the weight?To calculate, figure out the weight of the displaced water.
10Archimedes’ Principle Archimedes lived over 2000 years ago in Greece. He discovered the fact that:The buoyant force on an object is equal to the weight of the fluid displaced by the object.
11Sink or Float?The buoyant force determines whether an object will sink or float.If the buoyant force is greater than the weight of the object, then the object will floatIf the buoyant force is less than the weight of the object, then the object will sink.
12Sink or Float?An object floats when it displaces a volume of fluid whose weight is greater than or equal to its own weight.An object will float in a fluid if the density of that object is less than the density of the fluid.
13Why is the tip of the iceberg the only part seen out of the ocean?
14IsostasyThe buoyant force of the ocean pushes the iceberg upwards, but the volume of the ice is only slightly less than the same volume of salt water it displaces, so almost 90% of the iceberg remains submerged.
15Why do some objects sink while others float? Density (the object’s mass divided by it’s volume - how much space it takes up)In order for an object to float, the water it displaces must weigh more than the object itselfOr to put in density terms, the object must have a density lower than the density of the water
16If the density of water is 1g/cm3, then . . . will wood (D = 0.8 g/cm3) float?will aluminum (D = 2.7 g/cm3) float?will steel (D = 7.8 g/cm3) float?
17Didn’t you just say steel would sink?!? Then why is this ship made of steel floating on top of the water?
18The shell of the ship may be made of steel, but most of the space inside the hull is filled with air that has a very low density.
19Some creatures in the sea have gas filled bladders whose volume can be changed to adjust for the buoyant force at various depths.
20This is how submarines work too This is how submarines work too. They can take in sea water to submerge or discharge sea water to rise up to the surface.
21Can you think of something else that uses changes in the density within a chamber to make it rise or fall in our atmosphere?