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PHYSICS (slideshow) By:- Avipsit Rath Class:- 11th Sec:- “A” Roll:- “20” School:- Kendriya Vidyalaya Khurda Road NEWTON’s LAWS Sir Isaac Newton English mathematician and physicist Birth:- December 25, 1642 Death :-March 20, 1727 Place of Birth:- Woolsthorpe, England Known for Inventing, in part, the branch of mathematics now known as calculus Formulating the three laws of motion, which describe classical mechanics Proposing the theory of universal gravitation, which explains that all bodies are affected by the force called gravity. Career 1661 Entered Trinity College, University of Cambridge 1665-1666 Developed what he called the fluxional method (now known as calculus) while living in seclusion to avoid the plague 1669-1701 Served as Lucasian Professor of Mathematics at the University of Cambridge 1687 Published his seminal work, Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), which contained his three laws of motion and the theory of gravitation 1703-1727 Acted as president of the Royal Society, an organization that promotes the natural sciences 1704 Published Opticks (Optics), describing his theory that white light is a blend of different colors . NEWTON AND MECHANICS Sir Isaac Newton’s work represents one of the greatest contributions to science ever made by an individual. Most notably, Newton derived the law of universal gravitation, invented the branch of mathematics called calculus, and performed experiments investigating the nature of light and color. Newtonian Reflecting Telescope The first reflecting telescope was designed by Sir Isaac Newton in 1668. Starting about 1665, at the age of 23, Newton enunciated the principles of mechanics, formulated the law of universal gravitation, separated white light into colors, proposed a theory for the propagation of light, and invented differential and integral calculus. ROLE IN HISTORY OF PHYSICS The subsequent development of physics owes much to Newton's laws of motion, notably the second, which states that the force needed to accelerate an object will be proportional to its mass times the acceleration. If the force and the initial position and velocity of a body are given, subsequent positions and velocities can be computed, although the force may vary with time or position; in the latter case, Newton's calculus must be applied. This simple law contained another important aspect: Each body has an inherent property, its inertial mass, which influences its motion. The greater this mass, the slower the change of velocity when a given force is impressed. Even today, the law retains its practical utility, as long as the body is not very small, not very massive, and not moving extremely rapidly. Newton's laws of motion are three physical laws which provide relationships between the forces acting on a body and the motion of the body. NEWTON’s FIRST LAW The net force on an object is the vector sum of all the forces acting on the object. Newton's first law says that if this sum is zero, the state of motion of the object does not change. Essentially, it makes the following two points: An object that is not moving will not move until a net force acts upon it. An object that is in motion will not change its velocity (accelerate) until a net force acts upon it. IN OTHER WORDS:- Newton’s first law states “A body in motion remains in motion (with constant velocity) unless acted upon by an external force.” Rest, in Newton’s laws, is merely an example of motion with zero velocity. So force is defined as the agency that changes the state of motion, and thus the velocity, of a body. This is often paraphrased as "zero net force implies zero acceleration”. Law of Inertia NEWTON’s SECOND LAW The rate of change of momentum of a body is proportional to the resultant force acting on the body and is in the same direction. Using modern symbolic notation, Newton's second law can be written as a vector differential equation: where: is the force vector is mass is the velocity vector is time. Law of acceleration If the mass of the object in question is constant, as it always is in classical physics, this differential equation can be rewritten as: where: is the acceleration. Taking Special Relativity into consideration, the equation becomes where: m0 is the rest mass or invariant mass. c is the speed of light. Newton’s second law relates net force and acceleration. A net force on an object will accelerate it—that is, change its velocity. The acceleration will be proportional to the magnitude of the force and in the same direction as the force. The proportionality constant is the mass, m, of the object. F = ma NEWTON’s SECOND LAW In the International System of Units (also known as SI, after the initials of Système International), acceleration, a, is measured in meters per second per second. Mass is measured in kilograms; force, F, in newtons. A newton is defined as the force necessary to impart to a mass of 1 kg an acceleration of 1 m/sec/sec; this is equivalent to about 0.2248 lb. A massive object will require a greater force for a given acceleration than a small, light object. What is remarkable is that mass, which is a measure of the inertia of an object (inertia is its reluctance to change velocity), is also a measure of the gravitational attraction that the object exerts on other objects. The second law holds in the original form, which says that the force is the derivative of the momentum of the object with respect to time, but some of the newer versions of the second law (such as the constant mass approximation above) do not hold at relativistic velocities. NEWTON’s THIRD LAW Newton’s third law of motion states that an object experiences a force because it is interacting with some other object. The force that object 1 exerts on object 2 must be of the same magnitude but in the opposite direction as the force that object 2 exerts on object 1. If, for example, a large adult gently shoves away a child on a skating rink, in addition to the force the adult imparts on the child, the child imparts an equal but oppositely directed force on the adult. Because the mass of the adult is larger, however, the acceleration of the adult will be smaller. Law of Reciprocal Actions This law of motion is commonly paraphrased as: "To every action force there is an equal, but opposite, reaction force". All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction. To every Action there is always opposed an equal Reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. FOR EXAMPLE:- Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tyed to a rope, the horse (if I may so say) will be equally drawn back towards the stone: For the distended rope, by the same endeavour to relax or unbend it self, will draw the horse as much towards the stone, as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other. As shown in the diagram opposite, the skaters' forces on each other are equal in magnitude, and opposite in direction. Although the forces are equal, the accelerations are not: the less massive skater will have a greater acceleration due to Newton's second law. It is important to note that the action/reaction pair act on different objects and do not cancel each other out. The two forces in Newton's third law are of the same type, e.g., if the road exerts a forward frictional force on an accelerating car's tyres, then it is also a frictional force that Newton's third law predicts for the tyres pushing backward on the road. To every Action there is always opposed an equal Reaction. Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This law is often simplified into the sentence "Every action has an equal and opposite reaction". Newton’s third law also requires the conservation of momentum, or the product of mass and velocity. For an isolated system, with no external forces acting on it, the momentum must remain constant. In the example of the adult and child on the skating rink, their initial velocities are zero, and thus the initial momentum of the system is zero. During the interaction, internal forces are at work between adult and child, but net external forces equal zero. Therefore, the momentum of the system must remain zero. After the adult pushes the child away, the product of the large mass and small velocity of the adult must equal the product of the small mass and large velocity of the child. The momenta are equal in magnitude but opposite in direction, thus adding to zero. THANK YOU AND HAVE A NICE DAY. By:- Avipsit Rath

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