8th Class

Notes - Force and Pressure

Force and Pressure · A push or a pull on a body is called force. · A force can change the shape of an object, move the object, stop a moving object and change the direction of motion. · Force has magnitude as well as direction. · Some forces come into play when at least two objects interact. These forces are called contact forces. Muscular force and friction force are the examples of two such forces. Two important points about contact forces are as follows: § Forces applied on an object in the same direction add to one another. § If the two forces act in the opposite directions on an more...

Catgeory: 8th Class

Notes - Reaching the Age of Adolesence

Reaching the Age of Adolescence · Humans can reproduce only after growing up to a certain age called adolescence. It is a transitional stage of physical and psychological human development that generally occurs during the period from puberty to legal adulthood (age of majority). It is generally the age period of 11 years to 19 years. · At the age of adolescence, puberty sets in. The onset of puberty brings about growth of the reproductive organs. · The growth of hair at various places on the body, increase in height, development of breasts in girls, appearance of facial hair (moustache and beard) in boys are some of the changes that can be seen in adolescents. · The onset of puberty and maturity of more...

Catgeory: 8th Class

Notes - Reproduction in Animals

Reproduction in Animals · Reproduction is the biological process by which an individual organism gives birth to its young one. Animals can reproduce by two modes ?

(i) Sexual reproduction,

(ii) Asexual Reproduction.

· The mode of reproduction in which an individual can reproduce without involvement of another individual of that species is called asexual reproduction. · Sexual reproduction is the type of reproduction in which two individual, called parents, are needed to reproduce the young ones. · Human male reproductive system consists of a pair of testes (singular testis), more...

Catgeory: 8th Class

Notes - Cell-Structure and FUnctions

Cell - Structure and Functions · Cell is the basic structural unit of life. · Cells were first observed by Robert Hooke in 1665. He observed slices of cork (a part of the bark of a tree) under a simple magnifying device. He noticed partitioned boxes or compartments in the cork slice. · Cells are found in wide variety of shapes and sizes. Some cells are big enough to be seen with the unaided eye like egg of a hen while some are too small to be seen by the naked eyes like an amoeba. · Number of cells also varies from organism to organism. The organisms made of a single cell are called unicellular organisms while the organisms made of more than more...

Catgeory: 8th Class

Notes - Conservation of Plants and Animals

Conservation of Plants and Animals · Deforestation is one of the major environmental problems of the Present time. Deforestation leads to ail major environmental problems like desertification and global warming which consequently leads to floods or droughts. · Biosphere is the part of the earth in which living organisms exist or which supports life. · Biological diversity or biodiversity refers to the variety of organisms existing on the earth, their interrelationships and their relationship with the environment. · Species is a group of population which is capable of Interbreeding. · Plants and animals of a particular area are known as the flora and fauna of that area. · An ecosystem is made of more...

Catgeory: 8th Class

Notes - Microorganism-Friend and Foe

Microorganisms - Friend and Foe · Some organisms are too small to be visible by the naked eyes. These are called microorganisms. They may be unicellular or multicellular. · Microorganisms are found everywhere and in almost all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. · Microorganisms are also found inside human beings and other animals. · Microorganisms are classified mainly into five categories ? more...

Catgeory: 8th Class

Notes - Pollution of Air and Water

Pollution of Air and Water · Air pollution refers to the contamination of air by impurities like solid particles and gases in the air which may have a harmful impact on the living organisms and the non-living components. · An air pollutant is a substance that contaminates air and water. Pollutants can have adverse effects on humans and the ecosystem. Pollutants can be solid particles, liquid droplets, or gases. · Carbon monoxide, nitrogen oxides, carbon dioxide, methane and Sulphur dioxide are the major pollutants of air. · The greenhouse effect is the natural process by which the atmosphere traps some of the Sun's energy, warming the Earth enough to support life. Increasing levels of greenhouse gases like \[C{{O}_{2}}\] are leading to global warming. more...

Catgeory: 8th Class

Notes - Combustion and Flame

Combustion and Flame · Combustion is a process in which a substance reacts with oxygen to give off heat and light. · The substances which burn in air are called combustible substances while those that do not burn easily are called non-combustible substances. · The conditions required for combustion to take place are:

(i) bacteria,

(ii) fungi

(iii) protozoa and

(i) the presence of a combustible substance

(ii) the presence of oxygen and

(iii) heat to raise the temperature of the fuel beyond the ignition temperature.

· Coal and Petroleum · Natural resources can be classified into two types:

(i) inexhaustible or renewable resources and

(ii) exhaustible or non-renewable resources.

· Inexhaustible resources are the resources that are present in unlimited quantity in nature and are not likely to be exhausted by human activities. · Exhaustible resources are the resources that are present in limited amount in nature. They can be exhausted by human activities. Forests, wildlife, minerals, coal, petroleum, natural gas etc. are the examples of exhaustible natural resources. · Coal, petroleum and natural gas are more...

Catgeory: 8th Class

Notes - Materials-Metals and Non-Metals

Materials - Metals and Non-Metals · Materials can be classified into metals and non-metals. · Metals can be distinguished from non-metals on the basis of their physical and chemical properties. · Physical properties of metals § Metals are hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity. Iron, copper, aluminum, calcium and magnesium are some examples of the metals. · Metals are generally hard but the metals like sodium and potassium are soft and can be cut with a knife. Similarly, mercury is the only metal which is found in liquid state at room temperature. · Chemical properties of metals § Metals on more...

Catgeory: 8th Class

8th Class

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