Kepler's Law
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| Johannes Kepler Source : en.wikipedia.org |
1. The orbit of a planet is an eclipse with the Sun at one of the foci.
2. The line joining the planet and the Sun sweep equal areas in equal intervals of time.
3. The cube of the mean distance of a planet from Sun is proportional to the square of its orbital period T.
Gravitation
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| Issac Newton Source : scienceworld.wolfram.com |
Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. The force is along the line joining the centers of two objects. According to the universal law of gravitation, the force between two objects is directly proportional to the product of their masses. The universal law of gravitation successfully explained several phenomena which were believed to be connected :
- The force that binds us to the earth ;
- The motion of the planets around the Sun ; and
- The tides due to the moon and the Sun.
Gravitation is a week force unless large masses are involved. Force of gravitation due to the earth is called gravity.The force of gravity decreases with altitude. It also varies on the surface of the earth, decreasing from poles to the equator. The weight is equal to the product of mass and acceleration due to gravity.
In Brief : The law of gravitation states that the force of attraction between any two objects is proportional to the square of the distance between them. The law applies to objects anywhere in the universe. Such a law is said to be universal.
Buoyancy
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| Archimedes Of Syracuse Source : en.wikipedia.org |
The force due to the gravitational attraction of the earth acts on the bottle in the downward direction. So the bottle is pulled upwards. But the water exerts an upward force on the bottle. Thus, the bottle is pushed upwards.When the bottle is immersed, the upward force exerted by the water on the bottle is greater than its weight. Therefore it rises up when released.To keep the bottle completely immersed, the upward force on the bottle due to water must be balanced. This can be achieved by an externally applied force acting downwards. This force must be at least be equal to the difference between the upward force and the weight of the bottle.The upward force exerted by the water on the bottle is known as Upthrust or Buoyant Force. In fact, all objects experience a force of buoyancy when they are immersed in a fluid. The magnitude of this buoyant force depends on the density of the fluid.
Newton's Laws Of Motion
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| Issac Newton Source : scienceworld.wolfram.com |
1st Law ( Law Of Inertia )
Every body continues in its state of rest of uniform motion until it is acted upon by an external unbalanced force.
2nd Law
Newton' second law of motion gave the equation of force and direction of force.The rate of change of momentum is directly proportional to the force applied and change in momentum takes place in the direction of application of force.
Proof : Consider a moving body of mass (m) moving with an i.v = u. Let (a) force be applied on it for a short time "t" seconds (s) . Then its velocity changes to "v". Let "a" be the acceleration produced and "s" be the displacement.
3rd Law
" To every action there is always an equal and opposite reaction "
" To every action there is always an equal and opposite reaction "
- Sir Issac Newton
Though action and reaction are equal and opposite, they never cancel each other because they act on two different objects.
Application :
Recoil of a gun - When a bullet is fired from the gun , the bullet moves forward with muzzle velocity . Therefore, the gun acquires an equal backward momentum according to Newton's 3rd Law of Motion. This backward motion of the gun is called recoil of gun and that velocity is called recoil velocity.
Conservation Laws
All conservation laws such as conservation of momentum, energy, angular momentum, charge etc. are considered to be fundamental laws in physics. These are based on observations and experiments. It is important to remember that a a conservative law cannot be proved. It can be verified, or disproves, by experiment whose result goes against the law is enough to disapprove it. The law of conservation of momentum has been deduced from large number of observations and experiments. This law was formulated nearly three centuries ago. It is interesting to note that not a single situation has been realized so far, which contradicts this law. Several experiments of every - day life can be explained on the basis of the law of conservation of momentum.
Conservation Laws
All conservation laws such as conservation of momentum, energy, angular momentum, charge etc. are considered to be fundamental laws in physics. These are based on observations and experiments. It is important to remember that a a conservative law cannot be proved. It can be verified, or disproves, by experiment whose result goes against the law is enough to disapprove it. The law of conservation of momentum has been deduced from large number of observations and experiments. This law was formulated nearly three centuries ago. It is interesting to note that not a single situation has been realized so far, which contradicts this law. Several experiments of every - day life can be explained on the basis of the law of conservation of momentum.
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