8th Class

FACTORS AND MULTIPLES       FACTOR:

•             One Number is said to be a factor of another when it divides the other exactly.
•       If a number 'x' divides another number 'y' exactly, then we say that 'x' is a factor of 'y'.

  Example: more...

Crop Production and Microorganisms   Cultivation   Land preparation and cultivation methodology is among the basic factors which affect the yield of crops. For getting better yield, it is important to prepare land thoroughly, so that the weeds are destroyed and water absorption capacity of the soil is increased. Crops When the same kind of plants are grown in the fields on a large scale to obtain foods like cereals, pulses, vegetables and fruits, etc., it is called a crop.   Agriculture The growing of plants (or crops) in the fields for obtaining food is called agriculture. Crop production involves various agricultural practices such as:  

• Preparation of soil- It includes tilling, levelling and manuring of the fields.
• Sowing - good quality seeds are sown in the fields more...

Materials   Fibres A fibre is a piece of fabric that is long, thin and flexible. Plant fibres are the basis of febric such as cotton, silk and wool fibres come from animals. Many artificial fibres have also been invented such as rayon, nylon, polyester, acrylic, etc.  

• Rayon - is also known as 'artificial silk'. Cellulose which is obtained from wood pulp is the raw material to prepare rayon. It is used in home furnishings, suits, ties, blouses, sportswear, etc.
• Nylon - is entirely made of chemicals. It is very strong, elastic, light and water-resistant fiber. It is lustrous in appearance. It is used in making ropes, tents, fishing nets and parachutes.
• Polyester - is made from 'petroleum'. It is very strong, crease resistant, light, elastic and absorbs very little water. It is used in making pants, shirts, suits, jackets, more...

Coal and Petroleum   Coal   It is composed primarily of carbon and hydrogen along with small quantities of other elements, notably sulphur. It is a nonrenewable resource.   Coal Formation     Coal is a sedimentary rock formed from plants that flourished millions of years ago when tropical swamps covered large areas of the world. Lush vegetation, such as early club mosses, horsetails, and enormous ferns, thrived in these swamps. Generations of this vegetation died and settled to the swamp bottom and over time the organic material with a high percentage of carbon. Layers of mud and sand accumulated over the decomposed plant matter, compressing and hardening the organic material as the sediments deepened. Over millions of years, depending sediments layers, known as overburden, exerted tremendous heat more...

Conservation of Plants and Animals     Conservation is the sustainable use and protection of natural resources including plants, animals, mineral deposits, soil, clean water, clean air and fossil fuels such as coal, petroleum and natural gas. Natural resources are grouped into two categories: renewable resource is the one that may be replaced over the time by natural processes such as fish populations, natural vegetation or is inexhaustible such as the solar energy. Nonrenewable resources are those which are limited in supply and cannot be replaced even over extremely long period of time. The nonrenewable resources include fossil fuels and mineral deposits, such as iron ore and gold ore. Conservational activities for the nonrenewable resources focus on maintaining an adequate supply of these resources well in the future. Natural resources are conserved for more...

Cell Structure and Function   Cell Structure Cells fall into one of the two categories: prokaryotic or eukaryotic. In a prokaryotic cell, found only in bacteria and archaebacteria, all the components, including the DNA, mingle freely in the cell's interior, a single compartment. Eukaryotic cells, which make up the plants, animals, fungi and all other life forms contain numerous compartments or organelles within each cell. The DNA in eukaryotic cells is enclosed in a special organelle called the nucleus, which serves as the cell's command centre and information library. The term prokaryote comes from Greek word that mean "before nucleus" or "prenucleus," while eukaryote means "true nucleus."   Prokaryotic Cells Prokaryotic cells are among the tiniest of all cells, ranging in size from 0.0001 to 0.003mm in diameter. These cells, which can be rodlike, spherical or spiral in shape are surrounded by more...

Reproduction and Adolescence   Reproduction Reproduction is a process by which all living organisms produce off springs. Reproduction is one of the essential functions of plants, animals and other organisms for the preservation of the species. In almost all animals, reproduction occurs during or after the period of maximum growth.   Types of Reproduction   Asexual Reproduction It is a type of reproduction by which offspring arise from a single organism and it does not involve the fusion of gametes.   Types of Asexual Reproduction   Binary fission - in this type of reproduction the fully grown parent cell splits into two halves, producing two new cells. For example, amoeba and paramecium.    

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Force, Friction and Sound   Force A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force acting each of the objects. Force acting between objects can be placed into two categories:   Contact Forces Are those types of forces which result when the two interacting objects are perceived to be physically contacting each other.   Types of Contact Forces  

• Muscular Force - is the force exerted by the muscles of the body. This force can be applied to an object only when our body is in contact with the object, therefore muscular force is a contact force.
• Frictional Force - is the force which opposes the motion of one body over another body.

  Non-contact Forces Are more...

Chemical Effects of Current and Light   Chemical reactions are caused by passing of electric current through a conducting solution. This is called chemical effect of electric current.   Electric Current An electric current is a movement of charge. When two objects with different charges come in contact with each other and redistribute their charges, an electric current flows from one object to the other until the charge is distributed according to the capacities of objects. If two objects are connected by a material that lets charge flow easily, such as copper wire, then an electric current flows from one object to the other through then an Electric current is measured in ampere.   Conduction of Electric Current Through Liquids A solution of a substance or a substance in a liquid state which can conduct electricity is called an electrolyte. Most liquids that conduct more...

Solar System and Some Natural Phenomenon     Solar System Solar system, the sun and everything that orbits the sun, including the planets and their satellites, the dwarf plants, asteroids, kuiper belt objects and comets.   Solar System   Sun Sun is the closest star to the earth. Its average distance from the earth is about 150 million kilometres. It consists mainly of hydrogen and helium. Diameter of sun is about 1.4 million km. The temperature at its surface is about\[{{6000}^{o}}C\].   Planets Based on the distances of planets from the sun they are as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All the planets revolve around the sun in a fixed path called orbit. Planets which are close to more...