Section 3 2 BUOYANT FORCE Buoyant Force An

Section 3 -2 BUOYANT FORCE

Buoyant Force An upward force that fluids exert on all matter

Archimedes’ Principle The buoyant force is equal to the weight of the fluid that the object displaces (moves)

Weight versus Buoyant Force (p. 73) Sinking: An object will sink if the object’s weight is greater than the buoyant force Example: a rock in a lake

Floating: An object will float (suspended in fluid) if the object’s weight is equal to the buoyant force Example: A fish suspended in a lake

Buoying up: An object is buoyed up if the buoyant force is greater than the weight of the object Example: A duck “floating” on the surface of a lake

How does density affect floating or sinking? Objects that are denser than water/ air will sink Objects that are less dense than water/ air will float

Changing shape to change density Changing the shape of a metal into a hollow shape allows it to float because it will have more volume and will be less dense.

Changing mass to change density Changing the mass of an object will change its density Example: A submarine has “ballast tanks” that allow water in to change the mass and density of the sub

Changing volume Changing the volume of an object will change its density Example: Fish have “swim bladders” that change the volume and density of the fish ***The bladder fills with air to help the fish change position in the water