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Unformatted text preview: Chapter 4 Forces and Newton’s Laws of Motion 4.1 The Concepts of Force and Mass A force is a push or a pull. Contact forces arise from physical contact . Actionatadistance forces do not require contact and include gravity and electrical forces. 4.1 The Concepts of Force and Mass Arrows are used to represent forces. The length of the arrow is proportional to the magnitude of the force. 15 N 5 N 4.1 The Concepts of Force and Mass Mass is a measure of the amount of “stuff” contained in an object. 4.2 Newton’s First Law of Motion An object continues in a state of rest or in a state of motion at a constant speed along a straight line, unless compelled to change that state by a net force. The net force is the vector sum of all of the forces acting on an object. Newton’s First Law 4.2 Newton’s First Law of Motion The net force on an object is the vector sum of all forces acting on that object. The SI unit of force is the Newton (N). Individual Forces Net Force 10 N 4 N 6 N 4.2 Newton’s First Law of Motion Individual Forces Net Force 3 N 4 N 5 N 64 4.2 Newton’s First Law of Motion Inertia is the natural tendency of an object to remain at rest in motion at a constant speed along a straight line. The mass of an object is a quantitative measure of inertia. SI Unit of Mass: kilogram (kg) 4.2 Newton’s First Law of Motion An inertial reference frame is one in which Newton’s law of inertia is valid. All accelerating reference frames are noninertial. 4.3 Newton’s Second Law of Motion ∑ F Mathematically, the net force is written as where the Greek letter sigma denotes the vector sum. 4.3 Newton’s Second Law of Motion Newton’s Second Law When a net external force acts on an object of mass m , the acceleration that results is directly proportional to the net force and has a magnitude that is inversely proportional to the mass. The direction of the acceleration is the same as the direction of the net force. m ∑ = F a ∑ = a F m 4.3 Newton’s Second Law of Motion SI Unit for Force ( 29 2 2 s m kg s m kg ⋅ = This combination of units is called a newton (N). 4.3 Newton’s Second Law of Motion 4.3 Newton’s Second Law of Motion A freebodydiagram is a diagram that represents the object and the forces that act on it. 4.3 Newton’s Second Law of Motion The net force in this case is: 275 N + 395 N – 560 N = +110 N and is directed along the + x axis of the coordinate system. 4.3 4....
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This note was uploaded on 02/20/2010 for the course PHYSC 210 taught by Professor Uscinski during the Summer '09 term at American.
 Summer '09
 Uscinski

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