TCP/IP ( Transmission Control Protocol/ Internet Protocol)

Computer with the same network communicate with each other using their physical addresses, which are hard coded on the Network Interface Card (NIC) of a computer ( The NIC is a device that is attached to each of the workstations and the server, and helps the workstation establish the all important connection with the network). But these physical addresses can not be used across multiple networks. Different networks have different addresses lengths as well addressing formats. As we know, Internet is a network of many heterogeneous computer networks. This means that physical addressing would not work on the internet. Therefore, the concept of logical addresses is used in the internet to make it a virtual network. This logical address is the 32 bit IP address. However, at the lowest level, computers must still use physical addresses to communicate with computers on the same networks. Therefore we need a mechanism to convert a logical IP address to a physical address before the actual transmission can take place over a local network.

The TCP/IP  suite of communication protocols makes the internet a worldwide network of computers networks. Since TCP/IP  software is always the same across all computers connected to the internet, we can connect different computers running different operating systems, or better yet, different networks themselves.

TCP/IP  is a layered set of protocols. In order to understand what this means, it is useful to took at an example. A typical situation is sending mail, first, there is a protocol for mail. This defines a set of commands which one machine sends to another,  e.g., commands to specify who the sender of message is, whom iti s being sent to, and then the text of the message. However, this protocol assumes that there is a way to communicate reliably between the two computers. Mail, like other application protocols, simply defines a set of commands and messages to be sent. It is designed to be used together with TCP and IP . TCP is responsible for making sure that the commands get through to the other end. It keeps track of what sent, and retransmits anything that did not get through. Generally, TCP/IP applications use 4 layers :

1. An application protocol such as mail.
2. A protocol such as TCP that provides services needed by many applications
3. IP, which provides the basic service of getting datagrams (a datagram is a collection of the data that is sent as a single message) to their destination.
4. The protocols needed to manage a specific physical medium.

CITIZENS OF THE SEA

From Norway to New Zealand, from the frigid waters of the polar areas to the warm waters of the tropic, and everywhere in between, our seas and oceans teem with marine citizens that  prey, play, fight, survive, give birth in the water and continue the fascinating cycle of marine life.

Many fascinating creatures call the marine kingdom their home. One such creature is the Seahorse- the only animal species in which the male bears the unborn young! Some other interesting inhabitants of the sea are the Mimic octopus that changes its colour and shape in the blink of an eye and the leafy sea dragon that look like a plant! Whales and Dolphins are among the ocean's most intelligent citizens, while Loggerhead turtles, which travel 6000 km across the world's largest ocean braving hungry hammerhead sharks and other troubles to give birth to their young ones, are among its most persevering dwellers.

Some inhabitants of the aqua world have few interesting tricks up their sleeves to lure their prey. One such is the angler fish that lives in the dark, murky depths of the Atlantic and the Antarctic ocean. This angry looking fish swims around with its natural bait-a fleshy lobe tipped with luminous flesh protruding above its mouth! When any curious creatures comes to investigate this strange light glowing in the dark depths of the ocean, the angler fish quickly swallows it! other fascinating creatures include those that pump up and some that glow! When frightened the Puffer fish puffs up to a large ball several times ins normal size! A wonderful glow in the dark creature is the tiny Sea firefly that inhabits the coastal waters of Japan. These amazing creatures were harvested by the Japanese during the World War 2 to aid soldiers in reading maps and messages at night. Another interesting creature called the Flashlight fish has cheeks that glow! Marine creatures vary in size from tiny microscopic organisms to the Blue whale the largest animal on the planet.

The planet's first life form was born in the oceans. Not surprisingly, Oceans are home to about 80% of all life on Earth. Oceans are a treasure trove of life, and what makes them a world worth exploring and preserving is the astonishing diversity and the beauty of the citizens that call it home.

CHARLES AUGUSTIN de COULOMB

French  physicist, best known as for the formulation of Coulomb's law, Which states  that the force between two electrical charges is proportional to the product of the charges and inversely proportional to the square of the distance between them. Coulombic force is one of the principle forces involved in atomic interactions.

Coulomb developed his law as an outgrowth of his attempt to investigate the law of electrical repulsions  as stated by Joseph Priestly of England. To this end he invented sensitive apparatus to measure the electrical forces involved in Priestly's law and published his findings in 1785-89. He also established the inverse square law of attraction and repulsion of unlike and like magnetic poles, which become the basis for the mathematical theory of magnetic forces developed by Simeon- Denis Poission. The coulomb, a unit of electric charge, was named after Coulomb in his honour.

SURFACE ENERGY OF LIQUID

The molecules of a liquid are in a state of random motion inside the liquid. A molecule is attracted by other molecules lying within a range of  molecular force. A sphere of radius equal to the range of molecular force is called Sphere of molecular influence. The molecule at the centre of molecular influence is attracted equally in all the directions by all other molecules in the sphere.


For a molecule A, well inside the liquid, the forces of attraction on the molecule are equal in all directions. Hence net force on it is zero. consider a molecule B near the surface. In this case the sphere of molecular influence is partially outside the liquid. But the molecules within the liquid lying in the molecular influence attract the molecule B. So there is a net downward force.

Consider another molecule C on the surface of liquid. Half of the sphere of influence is outside the liquid. Hence the downward force on molecule is maximum. Thus when a molecule comes to the surface , it is doing work to over come this downward pull. The work done resides as potential energy in the molecule on the surface.

Thus  molecules on the surface of liquid have  potential energy. This energy is called the surface energy. To increase the area of a liquid, work has to be done. Thus energy is required to increase the surface area. The energy required to increase unit area of the surface is called the surface energy.

KEPLER'S LAWS OF PLANETARY MOTION

In 1543 Nicolaus Copernicus stated that all planets move around the sun in circular orbits with the sun at the center. But Johannes Kepler (1571-1630) discarded this theory and proposed the elliptical orbits for the planetary motion. he formulated three laws known as Kepler's law of planetary motion.




1)  KEPLER'S FIRST LAW (LAW OF ELLIPTICAL ORBIT)

       Every planet revolves round the sun in elliptical orbits, with the sun at one of the foci.     




2)   KEPLER'S SECOND  LAW ( LAW OD EQUAL AREA)

       The line joining the sun and the planet sweeps out equal areas in equal intervals of time.  i.e., the areal velocity swept by the radius vector of ellipse is a constant.




3)   KEPLER'S THIRD LAW ( HARMONIC LAW)

      The square of the time period of the revolution of planet around the sun is directly proportional to the cube of the mean distance between the sun and planet.