Archimedes was the son of an astronomer. He had traveled to Alexandria, Egypt, a place of great learning, where he studied the works of some other mathematicians, like Euclid and Conon. Archimedes was friends with King Hieron II of Syracuse. Archimedes helped his friend King Hieron II by creating machines for the king’s army. The pulley was one of these inventions, but Archimedes thought the study of mathematics was the most important thing he could do. Sometimes Archimedes got so busy thinking about mathematics that he forgot to take a bath and his servants would have to force him to go to the public baths.
Kings don’t like to be tricked. I’m sure you know this from all the stories you read when you were small. King Hieron II of Syracuse, was no exception. He worried that the people who made his crown charged him the price of using solid gold but instead they tricked him and used gold mixed with silver which costs less.
King asked the scientists to test his crown which is supposed to be made of pure gold. So Archimedes also thought of this crown testing. When Archimedes was at the public bath he noticed that when he climbed in to a soaking bath the water level went up. Archimedes knew he could use this knowledge to test whether King Hieron’s crown was made of solid gold. He was so excited about this new idea and he wanted to tell the king. He jumped out of the bath and shouted “Eureka!” which, is what you should shout whenever you have a great idea! Then Archimedes ran naked through the streets of Syracuse to tell the King his new idea.
This is how most of the principles will evolve so many of them have no scientific reason to evolve.
Principle: is a law of physics stating that the upward buoyant force exerted on a body immersed in a fluids equal to the weight of the fluid the body displaces. In other words, an immersed object is buoyed up by a force equal to the weight of the fluid it actually displaces.
buoyancy = weight of displaced fluid
Explanation: If an immersed object displaces 1 kilogram of fluid, the buoyant force acting on it is equal to the weight of 1 kilogram (as a kilogram is unit of mass and not of force, the buoyant force is the weight of 1 kg, which is approximately 9.8 Newtons.) It is important to note that the term immersed refers to an object that is either completely or partially submerged. If a sealed 1-liter container is immersed halfway into the water, it will displace a half-liter of water and be buoyed up by a force equal to the weight of a half-liter of water, no matter what is in the container.
If such an object is completely submerged, it will be buoyed up by a force equivalent to the weight of a full liter of water (1 kilogram of force). If the container is completely submerged and does not compress, the buoyant force will equal the weight of 1 kilogram of water at any depth, since the volume of the container does not change, resulting in a constant displacement regardless of depth. The weight of the displaced water, and not the weight of the submerged object, is equal to the buoyant force.
Formula:
- The weight of the displaced fluid is directly proportional to the volume of the displaced fluid.
- The weight of the object in water is less than the weight of object in air.
Suppose a rock’s weight is measured as 10 newtons when suspended by a string in a vaccum with gravity acting upon it. Suppose that when the rock is lowered into water, it displaces water of weight 3 newtons. The force it then exerts on the string from which it hangs would be 10 newtons minus the 3 newtons of buoyant force: 10 − 3 = 7 newtons. Buoyancy reduces the apparent weight of objects that have sunk completely to the sea floor. It is generally easier to lift an object up through the water than it is to pull it out of the water.
Therefore we can modify Archimedes statement as
apparent immersed weight =weight – weight of displaced fluid
This can be expanded like
Density/ Density of fluid =weight/ weight of displaced fluid
Density/ Density of fluid = weight/weight – apparent immersed wgt
This formula is used for example in describing the measuring principle of a dasymeter and of hydrostatic weighing.
Limitations: This principle will not consider surface tension effects.
0 komentar:
Posting Komentar