How Do We See ?

Introduction
We see with the help of eyes . When light enters the eye, it passes through the cornea, iris and lens before reaching the retina. In the retina, millions of light sensitive cells called rods and cones react to the light. This results in a series of complex chemical reactions. The se reactions form electrical impulses in the optic nerve, which sends them to the brain. The brain interprets these signals as an image.

Human Eye

Size
The eyes are small in size. Each eye is about 2.5 cm wide, 2.5 cm deep and 2.3 cm tall.

Socket and Lid
The eye socket is a bony cavity which contains the eyeball. The front part of the eye is protected by the eyelid, which keeps the eyes moist and clean.

Macula
Macula is a region of the retina. It is responsible for providing sharp vision and fine details that are required for reading and driving.

Lens
The eye lens is a biconvex lens with a diameter of about 1 cm. The lens is used to fine-tune vision.

How Do We Move Our Eyes ?

Introduction 
We move our eyes with the help of six muscles. The medial rectus muscle moves the eyes towards the nose. The lateral rectus muscle over the eyes towards the nose. The superior and inferior rectus muscles are responsible for upward and downward motion of the eyes. The superior and inferior oblique muscles help us to rotate the eyes.

Human Eye

Sclera
Sclera is the white part of the eyeball. Sclera is the outer covering and gives shape to the eyes. It has several blood vessels that provide blood.

Iris
Iris lies behind the cornea and gives colour to the eyes. Iris can change its shape with the help of several muscles attached to it.

Pupil
Pupil circle at the centre of the iris. The pupil allows light to pass into the eye.

Retina
Retina is the innermost layer of the eye. It provides vision by sensing light with the help of rod and cone cells. Rod cells are responsible for vision in low light and cone cells are responsible for colour vision and detail.

How Do Kidney Filter Blood ?

Introduction
Kidneys filter blood through the tiny filters, called nephrons. Nephrons are basic functional and structural units of kidneys. Each kidney has about one million nephrons. Nephrons have a tiny blood vessel called glomerulus interlinked with collecting tubule for urine. In the glomerulus, chemical exchange take s place where  urea, mineral salts, and toxins are filtered out from blood. This waste fluid is released from the body in the form of urine.

Kidney

Kidneys
Kidneys are bean-shaped organs located near the middle of back just below the rib cage. Kidneys are the main organs of the urinary system that filters blood.

Other organs
Other urinary organs are ureter, urinary bladder, and urethra, Urethra carries urine from kidneys to bladder. Urethra passes urine out of the body.

Urinary System
The urinary system is also responsible for maintaining normal blood pressure and controlling production of red blood cells.

Blood
Kidneys filter about 200 quarts of blood every day and produce 2 quarts of waste products and extra water that flows into the bladder.

How Fast Must a Spacecraft Go ?

Introduction
A spacecraft leaving the surface of earth needs to move at an incredible speed of over 40,000 kilometers per hour. The spacecraft is required to attain such great speed in order to break free of earths gravitational force. this speed is the earth's escape velocity, the minimum speed that and interplanetary spacecraft needs to escape the influence of earth's gravitational pull. The spacecraft requires abundant fuel to break through earth's gravitation.

Spacecraft Takeoff

Escape Velocity
Escape velocity depends upon the mass of the planet and the distance from the center of the planet to the space vehicle.

Calculation
The escape velocity of earth can be calculated using earth's mass, its radius and Newton's gravitational constant G.

Biggest Challenge
Achieving escape velocity is the biggest challenge that scientists face while launching a spacecraft.

Current Research
Scientists are working to create lighter space craft, more efficient fuels and new methods of propulsion, so that spacecraft do not face much difficulty in attaining great speeds.

How Does Satellite Transmit Information ?

Introduction 
Information is transmitted through artificial satellites called communication satellites. Communication satellites are used for telecommunications through signals transmitted from ground stations located on earth. Earlier, communication satellites traveled in a fixed orbit around earth but modern communication satellites can change their orbits. Television and radio programs, network are all made possible by satellite communication. Communication satellites are also useful in mobile applications to ship and airplanes. Digital data and telephone circuits are also relayed and carried through communication satellites.

Satellite Transmit Information

Arthur C. Clarke
Arthur C. Clarke was a British inventor and author who is credited for proposing the idea of satellite communication system in 1945.

Echo Satellite
Echo communication satellites were launched by the United States in the early 1960s.

Syncom II
Syncom II was the first communication satellite launched by NASA in 1963. The satellite achieved an orbit at 22,300 miles over the Atlantic.

DBS
Direct Broadcast Satellite (DBS) technology is used for Direct-To-Home satellite TV services, such as DirectTV or DISH Network. DBS Satellites orbit the earth to broadcast television or data signals.

How Do Deaf And Dumb People Communicate ?

Introduction
Deaf and Dumb people communicate by sign language. Sign language transmits messages by using hand movements, body postures, and facial expressions. Sign languages have very different grammatical structures as compared to spoken languages. Sign languages are also complex and hence not often written. Hundreds of sign languages are in use around the world. American Sign Language is the most commonly used sign language used by more than half a million deaf people.

Communication between deaf peoples

Fluency
One can attain fluency is sign language only after a long period of study and practice.

Finger spelling
Sign language uses finger spelling. Finger spelling is the way in which the shapes of alphabets are made on hands. Finger-spelling sis used by deaf people to spell  names of people, places and concepts.

Facial Expression 
Raising eyebrows, widening eyes and forwarding head are some of the facial expressions used in sign language.

Lip Reading
Lip reading is often thought  to be a essential part of sign language.

How Do Infants Communicate ?

http://howtogainaknowledge.blogspot.com/2016/04/how-do-infants-communicate.html

How Do Blind People Read And Write ?

Introduction 
Blind people read and write through Braille script. Braille script is a system of writing that uses raised dots to enable the blind people to read and write through sense of touch. The system consists of 63 characters, each having one to six raised dots arranged in six position matrix or cell embossed in lines of paper. Blind people move their fingers lightly over the copy to read the text. Louis Braille invented the system in 1824 when he was a student at the National Institute for Blind Children, Paris.

Blind people reading through Braille Book

Louis Braille
Louis Braille was born on Jan 4, 1809 at Coupvray near Paris. He was blinded at the age of three in an accident when he was playing with tools and tool slipped and plunged into his eye.

Charles Barbier
Charles Barbier, a French army officer, invented a system of tangible writing using dots in 1819 for night-time battlefield communications. Inspired by this, Braille developed a six-dot "cell" System.

Valentin Hauy
Valentin Hauy, a Frenchman, embossed paper as a means of reading for blinds for the first time by printing normal letters.

Adoption 
Louis Braille's system was officially adopted bu National Institute for Blind Children in Paris in 1854, two years after Louis Braille's death.