Cell - Structure and Functions * Cell - Structural and functional unit of life, is called cell. * Discovery of cell - Discovered by - Robert Hooke - Used - Thin slice of cork. - Cork - Part of bark of a tree * Egg of a hen represent single cell. * Multicellular organism -Organism made of more than one cells, is called multicellular organism. - Example- Human - Multicellular organism begins life as a single cell. * Unicellular organism - Single celled organism are called unicellular organism. - Example- Amoeba * Shape of cells Cell Shape Amoeba, WBC(White Blood Cell) Irregular shape Muscle cell Spindle shape RBC ...
Friction The force that opposes the relative motion between two surfaces in contact, is called friction. Factors affecting friction Weight of object Nature of surfaces in contact More the weight of object, more the friction. More smooth surface experience less friction. Importance of friction Friction helps in stopping object Friction helps to write, walk, Friction helps in all activities Friction produces heat. Harm cause by Friction Sole of shoes wear out. Machine parts get wear out. Friction can be increased by making surfaces rough. ( More rough means more interlocking between surfaces which means more friction ) Friction can be decreased by applying lubricant on surfaces. Friction can be decresed by changing shape of object. Rolling friction The force that oppose motion of rolling object, is rolling friction. Sliding friction The force that oppose moti...
Stars and Solar System Celestial objects The stars, the planets, the moons and many other objects in the sky are called celestial objects. Full Moon Day The day on which the whole disc of the moon is visible is known as full moon day. New Moon Day On the fifteenth day after full moon day, the moon is not visible. This day is known as new moon day. Crescent Moon The moon whose only a small portion appears in the sky, is called crescent moon. Phases of Moon The various shapes of the bright part of the moon as seen during a month are called phases of moon. The moon doesn't produce its own light. We see the moon because, the sunlight falling on it gets reflected towards us. The moon rotates on its axis. The moon revolve around the Earth. The moon has no atmosphere, no water, Star The sun is also a star. Sun appears larger than other stars. Because- -Stars are millions of times farther away than the sun....
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