Spinal Cord
The spinal cord is a thick cord of nerve tissue, which extends does form the brain stem. It is protected by the backbone. The spinal cord is responsible for the transfer of information between the brain and the rest of the body. It even controls the actions that do not involve the brain.
Nerves
A network of nerves runs throughout our body. Sensory nerves pass through the spinal cord and carry messages to the brain. Motor nerves carry messages back form the brain.
The automatic response of the body to an event is called a reflex action. Reflex actions are due to messages sent by the spinal cord. These actions are very fast.
For example, if you touch a hot object accidentally you withdraw your hand almost immediately. 
Brain
Brain is a very important organ. It controls our body movements and helps us to store information in our memory. The human brain has three parts
Cerebrum
It is the largest part of the human brain and is responsible for learning, memory, intelligence, and logic.
Cerebellum
It is situated below the cerebrum and is responsible for muscle coordination and for maintaining the balance of our body.
Medulla or the Brain Stem
It controls activities such as heartbeat, breathing, swallowing, and sneezing. 
Joints
A Joint is the place where two bones meet. Most joints are movable. There are four kinds of joints in our body.
Ball and Socket Joint
This type of joint allows movement in many directions. The shoulder joint and the hip joint are examples of ball and socket joint.
Hip Joint Knee Joint Elbow Joint
Hings joint
This type of joint works like the hinges in the door. This kind of joint only allows back and fourth movement. Bones in the knee, elbow/ fingers, and toes have this type of joint.
Pivot joint
This type of joint is found between the first two vertebrae of your backbone. It allows you to move your head up, down, and sideways.
Gliding Joint
This type of joint is found in the bones of the wrist and the ankle. It allows these bones to slide against each other in a gliding motion.
Wrist joint Ankle joint
Nervous System
The nervous system controls the different organs of our body.
Human Body
All organs work together to perform functions for the body. A group of organs doing some particular jot for the body form an organ system.
Human body has the following system performing certain function:
Respiratory system is responsible for carrying oxygen from the air to the bloodstream. Oxygen is necessary for human life.
Digestive system breaks the food we eat into smaller substances. After digestion, food can be used for producing energy.
Skeletal system gives shape to human body and helps in the movement.
Nervous system performs the functions of thinking, smelling/seeing, tasting etc.
Circulatory system helps in transportation of nutrients and other substances to various parts of the body.
Muscular system helps in movement.
Skeletal System
It is the framework of bones which gives support to human body. Adult human skeleton has 206 bones. Different parts of the human skeleton are.
Skull
Skull consists of 28 bones which protects the brain. All bones of skull are immovable except the lower jaw. With the help of movable lower jaw, we can talk and eat. In lower and upper jaw, we have teeth for cutting and chewing food.
Rib Cage
Ribs make a cage of bones around the chest which is called rib cage. It protects our internal organs. Generally adults have 12 pairs of ribs. There is a long bone at the centre of the chest which holds the ribs in place which is called as sternum. Ribs are attached to the backbone. Last two ribs are not attached to the sternum and are known as floating ribs. There floating ribs are attached to the backbone.
Backbone
It protects the spinal cord. It is made up of a series of small bones called vertebrae. Backbone is also called as vertebral column. Tigers, frogs and some other animals have backbone and are called vertebrates. Snails, earthworm and cockroaches like animals do not have a backbone and are called invertebrates.
Limbs
All human beings have two pairs of limbs: the forelimbs (arms) and hind limbs (legs). Thigh bone or fermur is the longest bone in the body.
Functions of the Skeletal System
The skeletal system has the following functions.
It gives shape and support to our body. Without the skeleton, our body would be floppy like a jelly. Forget about more... 
Simple Machines
Machines are simple tools which make our work easier and faster. They help us to do many work.
Some example of simple machines are lever, inclined plane, wheel and axle, pulley and screw.
Levers
Levers are commonly used tools like scissors, hammers and screw drivers.
When we life a rock with the help of a rod, the weight lifted by the person is the load and the force with which it is lifted is the effort. The point of contact of rod and the stone is the fulcrum.
Levers can be classified according to the portion of the fulcrum, the load and the effort.
When the fulcrum lies between the load and the effort, is called first class lever.
When the load is in between the fulcrum and the effort, it is a second class lever. When the effort is in between the fulcrum and the load, it is a third class lever.
Inclined Placed
An inclined place is a slope which makes work easier. When workers have to load or unload a truck they use a plane of wood as an inclined plane.
The Pulley
A pulley is a small wheel with a groove around its outer edge. There are two types of pulleys a fixed pulley and a movable pulley. The pulley used for drawing water from a well is a fixed pulley movable pulleys along with fixed pulleys are used to lift loads.
The wheel and axle
A wheel attached with a rod attached to it is known as a what-and axle arrangement. It is easier to push a load on wheels than carrying it. This arrangement is used in vehicles. Sewing machines and cycles.
The Screw
Screw is a tool used to gold things tightly together. Bigger screws called screw jacks are used to lift cars and other heavy objects. When two things are joined by a screw, they are held together through a long distance while when we join things with a nail, they are held together only through the length of the nail.
Consider the following statements:
Statement: 1. Energy is the capacity to do work.
Statement: 2. Energy is the exerted force on a body.
Which one of the following is correct about the above statements?
(a) Both statements are true
(b) Both statements are false
(c) Statement 1 is true and 2 more... 
Energy
We require energy to do work. We get lots of nutrients from plants and animals, which are the source of energy. These nutrients in our body is digested and give us energy. A small animal like ass cannot carry load equal to the load carried by an elephant. Hence, the energy is the capacity to do work. Every movement in our universe is carried out by the consumption of energy.
Therefore, we need different forms of energy to do various types of work. Heat energy is required to boil the water. Our voice and sound produced by the different objects possess sound energy. Mechanical energy is required to lift and or move an object. We use muscular energy to move our body. A bulb in our house works on electrical energy. Mechanical energy is further divided into two groups, kinetic and potential energy.
Kinetic Energy
The energy that an object possesses by its motion is called kinetic energy. A stone thrown on the glass, breaks the glass due to kinetic energy. A ball hits the stamps due to the kinetic energy. Therefore, a moving object possesses kinetic energy. Kinetic energy of a moving object is depends on the mass of the object. If the mass of the object is more, it possesses greater kinetic energy.
If we throw an iron ball slowly on a soft piece of land, the ball will float on the surface. If thrown fast then the ball will dig the land and will enter into the lower surface. Hence, the kinetic energy of an object is dependent on the speed of the object.
Look at the following picture of examples of kinetic energy:
A running car possesses kinetic energy
A running boy possesses kinetic energy
Potential Energy
When a body is placed at certain height from the surface of the earth, the energy it possesses is called potential energy. The formula to calculate the potential energy is m x g x h. Where, m = mass of the body, g = gravitational pull by the earth and h = height of the body from the surface of the earth.
Therefore, the potential energy of a body depends on the mass and height at which the body is placed from the surface of the earth. The potential energy will increase on increasing the height from the surface of the earth and also the mass of the body.
Look at the following picture, the example of potential energy::
In the above picture a ball of mass m is placed at the height of h. The ball possesses potential energy and energy possesses by the ball is calculated by the formula: product more... 
Force
A push or pull acting on an object is called a force.
A force can be used to:
Move a stationary object
Stop a moving object
Make a moving object move faster
Slowdown a moving object
Change the direction of a moving object
Change the shape and size of an object
Type of Force
There are different types of forces
Muscular Force
When something has to be pushed, pulled or lifted, muscular force is applied.
Gravitational Force
Because of gravitational force, we are able to stay on the ground.
Frictional Force
Frictional force slows down a moving object. Even frictional force helps us in walking.
Elastic Force
A stretched rubber band regains its original position on being released because of elastic force. Elastic force arises when a baby deforms.
Mechanical Force
Simple tools makes use of mechanical force.
Buoyant Force
The upward push of water on a floating object is called buoyant force or up thrust. If we push a mug or piece of wood, we can feel an upward thrust. 
Introduction
When a force is applied on a body, it may or may not move. If the applied force is sufficient to move the object from one place to another, it is said that the work has been done. If the applied force is not sufficient to move the object from one place to another, then no work has been done. Energy is the capacity to do work. In this chapter we will study about the work and energy.
Work
Whenever an applied force is capable to move an object, on which the force is applied, the work is done. A boy moves a chair from one place to another by applying force that means the work is done. The same boy applies a force on the wall to move it from one place to another and wall cannot move, hence, no work is done.
The following are the conditions for the work to be done:
In the picture above a body "A", moves from one place to another by the application of force. Therefore, the work is done.
In the picture above, a man is pushing the door but the door does not change its position, hence no work is done.
Unit for the Measurement of Work
The unit for the measurement of work is joule which is also expressed by 'J'. The unit of work is derived from the product of applied force on a body and displacement of the body due to the applied force. Therefore, we can say that if a force of 1 N acting on a body and body moves 1 m in the direction of the applied force then 1 J of work is done. Hence, according to the work done, 1 J = 1 N (Applied force) x 1 m (Displacement) = Mm (Newton metre).
Find the work done if a body moves through a distance of 5 m in the direction of applied force of 100 N.
(a) 500J
(b) 400J
(c) 1000J
(d) 300J
(e) None of these
Answer: (a)
Explanation
Work done = Force x Displacement = 100 N x 5 m = 500 Nm = 500 J.
Therefore, option A is correct and rest of the options is incorrect.
How much work is done on lifting a body of 1 kg up to the distance of 1 m above the ground or vertically?
(a) 5.6 J
(b) 2.3 J
(c) 100 more... 
Sound
Sound is a form of energy that gives the sensation of hearing. The sound that reaches your ear travels through the air.
Human Ear
Sound waves enters into ear and vibrates the eardrum, these vibrations are carried to brain through the nerves. Brain interprets the sound and sends the message to the receptor through motor nerve. There are 3 small bones in the ear. These are malleus, incus and stapes. Stapes is the smallest bone in the body lies in our ear.
Pleasant Sounds
Unpleasant Sound
Reflection of sound
Reflection of sound waves is the phenomena of bouncing off sound waves to the same medium, after striking the surface. Sound waves also follow the law of reflection, as followed by light waves. Sound waves can be reflected from walls of building, root, clefts etc.
Sound waves on striking a surface can:
Reflect from the surface.
Diffract around an obstacle.
Diffraction phenomena — Unlike light rays, sound wave does not travel in straight line, rather it bends and scatters around obstacles like corners of doors, windows opening etc. A diffraction phenomenon enables us to hear the conversation of the people sitting in adjacent room, as sound waves manage to reach us through the door openings.
Echo
Echo phenomena occurs when the reflected sound waves reaches the source in more than 0.1 seconds after the original sound wave was produced. When we talk in an empty room, we'll hear our talk after a short while. This occurs because of the reflection of the sound waves back towards the source in 0.1 sec. Echo can't be heard everywhere. For echo to be heard, at least the distance of source from the reflecting surface should be 17.2 m.
The reflected sound can be heard only if it takes more than 0.1 sec to reach the observer.
Absorption of sound waves (Acoustics): It means the absorption of sound waves by a material. A surface that absorbs sound waves does not reflect them. A good sound absorber is generally a porus material i.e. glass, wool etc.
Levels of Sound
Sound is measured in decibel. A table is given below in which source of sound and decibels are given.
Shadow Formation
Shadow is formed when opaque objects come in between light source and the screen (Which can be ground, wall etc.).
Light always casts shadows of the opaque objects placed in its path. The size and direction of the shadow depend on the direction and distance of the light coming from the source.
Shadow formation reveals that light always travels in a straight line and the portion through which light can't pass through becomes dark, which is called shadow. The direction of light source affects the direction of shadow formation.
Shadows are always black and represent the outline of the object.
Conditions necessary for the formation of shadow:
Source of light
An opaque object.
Screen on which shadow is formed.
Internal structure of eye
Look at the following picture of parts of eyes and their functions:
Shruti is surprised to see the light phenomena in National Science Centre where the different types of images of a person are seen in a mirror. Which branch of science she should study to understand the reason behind this?
(a) Acoustic
(b) Optics
(c) Zoology
(d) Astronomy
(e) Botany
Answer: (b)
Explanation
Number of images formed would depend on the angle between the mirrors, infinite images are formed when two mirrors are placed parallel to each other. Therefore, option (B) is correct and rest of the options is incorrect.
Thunder storm and lightening
(a) Dimpy
(b) Ashoo
(c) Both are correct
(b) Both are incorrect
(e) None of these
Answer: (b)
Explanation
Speed of light is faster than the speed of sound, hence lightening is seen first than thunderstorm. Therefore, option (B) is correct and
rest of the options is incorrect. 
