FORM 4: 3.5 APPLYING ARCHIMEDES' PRINCIPLE

THE MEANING OF BUOYANT FORCE

The buoyant force is the upward force resulting from an object being wholly or partially immersed in a fluid.

RELATIONSHIP BETWEEN BUOYANT FORCE AND WEIGHT OF FLUID DISPLACED

Buoyant force = W₁ – W₂

Weight of fluid displaced = W₃

It is found that, buoyant force = weight of fluid displaced

ARCHIMEDES’ PRINCIPLE

Archimedes’ Principle states that when an object is wholly or partially immersed in a fluid, it experiences a buoyant force equal to the weight of the fluid displaced.

APPLICATIONS OF ARCHIMEDES’ PRINCIPLE

§          When a submarine is diving into the sea, the valves of the ballast tank open to allow water to enter.

§          Thus, its overall weight is bigger than the buoyant force, allowing it to dive.

§          When a submarine rises to the surface of the sea, the ballast tank is pumped with compressed air and water is forced out of the tank through the open valves.

§         Thus, its overall weight is smaller than the buoyant force, allowing it to rise to the surface. 

§         Hydrometer is used to determine the relative density of liquids.

§         The upthrust of the liquid causes the hydrometer to float.

§         The higher the density of the liquid, the bigger the upthrust will be. Thus, the scale of the hydrometer increases in a downward direction.

§         Big bulb enables hydrometer to float.

§         Small bulb filled with lead enables the hydrometer to float vertically.

§        Thin stem of hydrometer increases the sensitivity.

§         Prior to departure, the air inside the balloon is heated by the gas flame to a temperature above 00 ^oC.

§         The air inside the balloon expands and part of it out of balloon through the hole below it.

§         Thus, the total weight of the balloon decreases.

§         If the total weight of the balloon is smaller than the buoyant force, it would be accelerated upwards.

§         Ships are marked with the Plimsoll line for safety purposes.

§         Due to different temperatures and salinity concentrations, the density of sea water at different parts of the world varies.

§         The Plimsoll line will help navigators to determine the safety level that ships can lie in the water and still be safely loaded under different conditions.