Buoyancy Why do objects sink or float Buoyancy

Buoyancy Why do objects sink or float?

Buoyancy �Why do some things sink, while others float? �When an object is placed in a fluid, the fluid presses on the object in all directions. �Buoyancy is the upward force that a fluid exerts on an object. �Buoyancy determines whether an object will sink or float. �Buoyancy depends on weight, fluid displacement, shape and density.

Weight and Fluid Displacement �When an object is put in a fluid, it displaces a certain amount of fluid. �The weight of the displaced fluid equals the upward buoyant force (Archimedes’ Principle). �An object floats if it displaces an amount of water greater than or equal to its own weight. �An object sinks if it displaces an amount of water less than its own weight.

Shape �An object’s shape affects the amount of fluid it displaces. Therefore, an object’s shape affects its buoyancy. �A screw does not displace much water, so the buoyant force acting on it is very small. �The buoyant force cannot support the weight of the screw, so the screw sinks.

Shape �A ship has a large hollow shell and displaces a lot of water, so the buoyant force acting on the ship is large. �The buoyant force can support the weight of the ship, so the ship floats. Force of gravity Buoyancy force

Density �The density of the fluid also affects buoyancy. �Denser fluids exert a greater buoyant force.

Upward Lift • You Will Need: • 2 tall drinking glasses • Water and a container of salt • 2 uncooked eggs • Procedure: • Fill both glasses half full with water. • Mix about 10 heaping teaspoons of salt into one of the glasses of water. • Add one egg to each glass of water. (Caution: Always wash your hands after touching an uncooked egg. It may contain harmful bacteria. ) • Observations: • Explain what you observed and why you think this

Observations • A denser liquid has a greater upward lift or buoyancy. Salt makes water denser. • The egg floats in the salt water because it is less dense than the salt water. • The egg sinks in the fresh water because it is denser than the fresh water. • This is why ships ride higher in ocean water than in fresh water and why it is easier to swim in the ocean than in a lake.