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Transcript
Newton’s Laws of Motion - 1 Classical Mechanics Describes the relationship between the motion of objects in our everyday world and the forces acting on them. Conditions when Classical Mechanics does not apply: - Very small objects (< atomic sizes) - Objects moving near the speed of light Forces Simple definition: a force is a push or pull on some object. Force is a vector quantity. Distunguish: contact forces and remote (“action at a distance” or “field” forces. Contact forces result from physical contact between two objects. Field forces act between disconnected objects. Examples of Contact and Field Forces The Four Fundamental Forces In order of decreasing strength: Strong nuclear force Electromagnetic force Weak nuclear force Gravity All are field forces. Only gravity and electromagnetic forces are treated in classical mechanics. Lex 1: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare. Law 1: Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. Law 1: Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. This is sometimes called the law of inertia. Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur. The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body. Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur. The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body. F a m Second Law: F a m 1. The acceleration vector is in the direction of the net force. 1. a is in the direction of a F 1 a m F Second Law: F a m 2. The magnitude of the acceleration vector is proportional to the magnitude of the net force. a is in the direction of 2. a F 1 a m F Second Law: F a m 3. The magnitude of the acceleration vector is inversely proportional to the mass. a is in the direction of a 3. F 1 a m F The SI unit for force: The force that gives an object of 1 kg mass an acceleration of 1 m/s2 is defined as 1 newton (N). 1 N = 1 kg.m/s2