1st Principle: Archimedes' Principle

Archimedes' principle states that a body which is wholly or partially immersed in a fluid is acted on by an upward force equal to the weight of fluid displaced. The upward force is called an upthrust. The resultant force on the body is the difference between the upthrust and body's weight. This difference is zero for a floating body.The first diagram shows a brick under water.The bottom of the brick is lower than the top and the water pressure acting on the bottom of the brick is slightly greater than the water pressure acting across the top. The upward thrust FB exceeds the downward thrust FA. The difference between these two thrusts, (FB-FA) is the upthrust exerted by the water on the brick. If the brick were replaced by an equal volume of water, the new mass of water would keep quite still. The weight of this new mass of water is just equal to the upthrust (FB-FA). The weight of the displaced water just equals the upthrust on the brick. the second diagram applies the same ideas to a block of wood floating on water. Here the upthrust equals the weight of the wood, which equals the weight of water displaced, and this is known as the law of flotation. What is the true for a brick under water or for a block of wood floating on water is true for any kind of body immersed in any kind of fluid or floating upon it. Secara kesimpulannya, Archimedes' principle ini berkait rapat dengan Bouyancy dan amount of water displaced apabila kita letakkan bongkah kayu ke dalam air,, maka jumlah air yang displaced itu sama dengan kayu yang diletakkan. Notice the principle is about the weight of fluid displaced. Archimedes' principle will not operate in weightless circumstances, like a spacecraft.