UPSC CIVIL SERVICES RESULT 2015-2016

GENERAL SCIENCE-MOTION AND THREE(3) LAWS OF MOTION- NOTES FOR EXAM


MOTION AND THREE(3) LAWS OF MOTION

In this topic you will learn about Motion ,three laws of motion ,quantum mechanics  etc .Motion and laws of motion is one of the most important topic in  science ,you will easily find its practical application in our day to day life.
So you can’t ignore this topic if you are preparing for any exam.


  • Motion is a change in position of an object with respect to time and its reference point.
  • Motion is typically described in terms of velocity, acceleration, displacement, and time.
  • A body which does not move is said to be at rest, motion-less, immobile, stationary,or to have constant (time-invari-ant) position.
  • An object's motion cannot change unless it is acted upon by a force, as described by Newton's first law.
  • Motion in the universe is described through two sets of apparently contradictory laws of mechanics.
  • Motions of all large scale and familiar objects in the universe (such as projectiles, planets, cells, and humans) are described by classical mechanics.
  •  Whereas the motion of very small atomic and sub-atomic objects is described by quantum mechanics.
Classical Mechanics    
  •  Classical mechanics is used for describing the motion of macroscopic objects, from projectiles to parts-of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies.
  • Classical mechanics is fundamentally based on Sir Isaac Newton's Laws of Motion.
  • Newton first presented his  three laws of motion in the "Principia Mathematica Philosophiae Naturalis" in 1586.

 Newton's First Law of Motion
Newton's First Law of Motion,laws of motion
Newton's First Law of Motion (img credit-NASA)

  • Newton's first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.  This is normally taken as the definition of inertia.
  • The key point here is that if there is no net force acting on an object (if all the external forces cancel each other out) then the object will maintain a constant velocity.
  •  If that velocity is zero, then the object remains at rest. If an external force is applied, the velocity will change because of the force.
  • There are many excellent examples of Newton's first law involving aerodynamics.
  •  The motion of an airplane when the pilot changes the throttle setting of the engine is described by the first law.
  • The motion of a, ball falling down through the atmosphere, or a model rocket being launched up into the atmosphere are both examples of Newton's first law.
  • The motion of a kite when the wind changes can also be described by the first law.

Newton's Second Law of Motion
Newton's Second Law of Motion (img credit-NASA)

  •  The second law explains how the velocity of an object changes when it is subjected to an external force.
  • The law defines a force to be equal to change in momentum (mass times velocity) per change in time
  •  This is the most powerful of Newton's three Laws, because it allows quantitative calculations of dynamics: how do  velocities change when forces are applied.
  •  Newton also developed the calculus of mathematics, and the changes expressed in the second law are most accurately  defined in differential forms (Calculus can also be used to determine the velocity and location variations experienced by an object subjected to an external force.)
  •  For an object with a constant mass m, the second law states that the force F is the product of an object's mass and its acceleration a: F = mxa
  • For an external applied force, the change in: velocity depends on the mass of the object.
  • A force will cause a change in velocity; and likewise, a change in velocity will generate a force. The equation works both ways.

Newton's Third Law of Motion
Newton's Third Law of Motion
Newton's Third Law of Motion (IMG credit- NASA)


  • The third law states that for every action (force) in nature there is an equal and opposite reaction.• In other words, if object A exerts a force on object B, then object B also exerts an equal force on object A.
  •  Notice that the forces are exerted on different objects.
  •  The third law can be used to explain the generation of lift by a wing and the production of thrust by a jet engine.
  • Newton's three laws of motion, along with his law of universal gravitation, explain Kepler's laws of planetary motion, which were the first to accurately provide a mathematical model or understanding orbiting bodies in outer space.
  • This explanation unified the motion of celestial bodies and motion of objects on earth.
  • Classical mechanics was later further enhanced by Albert Einstein's special relativity and general relativity.

Quantum mechanics
  •  Quantum mechanics is a set of principles describing physical reality at the atomic level of matter (molecules and atoms) and the subatomic (electrons, protons, and even smaller particles).
  •  In contrast to classical mechanics, where accurate measurements and predictions can be calculated about location and velocity, in the quantum mechanics of a subatomic particle, one can never specify its state, such as its simultaneous location and velocity, with complete certainty (this is called the Heisenberg uncertainty principle).
  •  In addition to describing the motion of atomic level phenomena, quantum mechanics is useful in understanding  some large scale phenomenon such as superfluidity, super-conductivity, and biological systems, including the function of smell receptors and the structures of proteins.

            
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