The universe
The universe has unlimited size and unknown shapes.All the existing things including different galaxies, constellations, planets, satellites, comets, meteors, meteorites, asteroids etc.constitute it.Our earth is a planet, which is a member of the solar system.The solar system is situated in a galaxy called milky way.The milky way is a medium size galaxy,which consists of about 150 billions of stars. Astonomers believes that there are about 10 power 12 such galaxies in the univers. Now you can imagine that how hug the universe is.Because of its so huge and unlimited size,the distance between two heavenly bodies is inconvenient to measure in metres and kilometres. Hence, astronomical unit(AU), Light year(LY) and parsec are used to measure the distance in the universe.
1 AU= 1.5*10 power 11 m
1 LY= 9.46*10 power 15 m
1 Parsec = 3.26 Ly
Solar system
Only the sun is a known star, which has a group like solar family and only one planet the earth of it has suitable conditions for organisms to survive on it. The solar system consists of the sun and all the objects around it are influenced by its gravity.These objects include planets, dwarf planets and satellites. Countless other smaller objects such as meteroids (meteors and meteorites), and an electrically charged gas the sun. Drifting particles called interplanetary dust and an electrically charged gas known as plasma exist in the space of the solar system. Although solar system is huge, it is only a small part of a galaxy. The eight planets of the solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The international convention of astronomers held on 2006 in Prague of Czech Republic has removed the Pluto from the list of planets.A new definition of planet is also given by the convention. According to it:
1.A planet should have its own round orbit (elliptical) around the sun.
2.Its shap must be round.
3.Its orbit must not cross the orbit of other planets.
The Pluto fails to fulfill the last condition, due to which it is kept in the category of Dwarf planets.Eris and Ceres are also kept under this category.
In the solar system,the asteroids belt lies between the orbits of Mars and Jupiters.
Friday, May 13, 2016
Thursday, May 5, 2016
Force
Consider a pen is lying on a table.It continues to be lying on the table at the same position until someone displaces it to other position. From moving it, one has to either puss or pull it Such push or pull on a body i called force Thus,to bring a body into motion from the state of rest,any force has to act on it.
Consider a situation in which a ball is rolling on the ground. We observe that the ball finally stop after covering a certain distance.It will cover longer distance if the ground is made smoother.We can well assume that when the ground is perfectly smooth, the ball would continue moving forever in the same direction with a constant speed.It is the roughness of the surface that provides opposing force called friction,to stop the ball from moving.Thus,to bring a body into rest from the state of motion,force has to act on it in opposite direction of its motion.
Consider a very big stone at rest to which boy cannot move by pushing or pulling it.This means, the force exerted by the boy is insufficient to move the stone.Similarly, a moving body cannot be stopped if the applied force is insufficient.Only sufficient force can do this.A body having a small mass requires less force to move or to stop.
Thus, force is that push or pull on a body that changes or tends to change the state of rest or of uniform motion in a straight line.
Force acting on a body can do the following things:
1.It can change the speed of the body.
2.It can change the direction of motion of body.
3.It can change the shape and size of the body.
4.I t can change the position of the body.
The SI unit of force is newton(N).In CGS system,the unit of force is dyne.
1 Newton=100000 dynes.
Force is measured bu using a spring balance or a top pan balance.
Balanced and unbalanced forces
When a number of forces acting on a body do not change its state of rest or uniform motion in a straight line,the forces are said to be balanced forces.For example, in the game of tug of war,two teams pull a rope in opposite directions.When the two teams exert equal and opposite forces on the rope,the rope remains steady and does not move in any direction.It appears as if no force is acting on the rope.Thus, the two forces acting on the rope in this case are balanced forces.
When a number of forces acting on a body change its state of rest or uniform motion in a straight line,the forces are said to be unbalanced forces.For example,if we push a toy car towards east,it moves towards east.If it is pushed towards west,it moves towards west.This unbalanced force produces motion.
Inertia
The property of a body due to which it remains or tends to remain in the state of rest or uniform motion in a straight line unless an unbalanced force act on it, is called inertia.Only unbalanced force can change the state of rest of the state of motion and vice versa.Because of this property of the body,it opposes any change in its state of rest or of uniform motion in a straight line.
Consider a very big stone at rest to which boy cannot move by pushing or pulling it.This means, the force exerted by the boy is insufficient to move the stone.Similarly, a moving body cannot be stopped if the applied force is insufficient.Only sufficient force can do this.A body having a small mass requires less force to move or to stop.
Thus, force is that push or pull on a body that changes or tends to change the state of rest or of uniform motion in a straight line.
Force acting on a body can do the following things:
1.It can change the speed of the body.
2.It can change the direction of motion of body.
3.It can change the shape and size of the body.
4.I t can change the position of the body.
The SI unit of force is newton(N).In CGS system,the unit of force is dyne.
1 Newton=100000 dynes.
Force is measured bu using a spring balance or a top pan balance.
Balanced and unbalanced forces
When a number of forces acting on a body do not change its state of rest or uniform motion in a straight line,the forces are said to be balanced forces.For example, in the game of tug of war,two teams pull a rope in opposite directions.When the two teams exert equal and opposite forces on the rope,the rope remains steady and does not move in any direction.It appears as if no force is acting on the rope.Thus, the two forces acting on the rope in this case are balanced forces.
When a number of forces acting on a body change its state of rest or uniform motion in a straight line,the forces are said to be unbalanced forces.For example,if we push a toy car towards east,it moves towards east.If it is pushed towards west,it moves towards west.This unbalanced force produces motion.
Inertia
The property of a body due to which it remains or tends to remain in the state of rest or uniform motion in a straight line unless an unbalanced force act on it, is called inertia.Only unbalanced force can change the state of rest of the state of motion and vice versa.Because of this property of the body,it opposes any change in its state of rest or of uniform motion in a straight line.
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