Archimedes' Principle

Definition

Object that is partially or totally submerged in a fluid will experience a buoyant force equal to the weight of the fluid of the object displaced

Application

+ submarine floats or submerges by changing its buoyancy
+ ballast tanks control its buoyancy
+ when ballast tank is full of air, submarine is less dense than the water(float)
+ to submerge, submarine opens the vents on top of the ballast tanks
+ seawater fills the ballast tanks and forces air out of the vents
+ submarine is now dense than the water(sink)
+ the depth can be controlled by adjusting the water to air ratio in ballast tanks
+ to make submarine rise, compressed air is blown into ballast tanks forcing the seawater out
+ submarine becomes less dense(rise)

Hydrometers

+ used to determine density of liquid
+ thin glass tube closed at both ends
+ if the density of liquid is greater, the object floats higher
+ if hydrometer floats deeper, the liquid has low density

Hot-air Balloons

+ inside air balloon is heated by external burner
+ hot air < cold air = balloon floats
+ buoyancy of balloon controlled by the burner