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ch04-newtons-law-of-motion

# ch04-newtons-law-of-motion - MasteringPhysics Assignment...

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10/13/08 1:10 AM MasteringPhysics: Assignment Print View Page 1 of 13 http://session.masteringphysics.com/myct/assignmentPrint?assignmentID=1157496 [ Print View ] Introductory mechanics Chapter 04 - Newton’s Laws Of Motion Due at 11:59pm on Tuesday, September 30, 2008 View Grading Details Newton's 1st Law Learning Goal: To understand Newton's 1st law. Newton's Principia states this first law of motion: An object subject to no net force maintains its state of motion, either at rest or at constant speed in a right line. This law may be stated as follows: If the sum of all forces acting on an object is zero, then the acceleration of that object is zero. Mathematically this is just a special case of the 2nd law of motion, when , prompting scholars to advance the following reasons (among others) for Newton's spelling it out separately: 1. This expression only holds in an inertial coordinate system--one that is not accelerating--and this law really says you have to use this type of coordinate system (i.e., Newton's laws won't work inside an accelerating rocket ship.) 2. This was a direct challenge to the Impetus theory of motion, described as follows: A mover, while moving a body, impresses on it a certain impetus, a certain power capable of moving this body in the direction in which the mover set it going, whether upwards, downwards, sideways or in a circle. By the same amount that the mover moves the same body swiftly, by that amount is the impetus that is impressed on it powerful. It is by this impetus that the stone is moved after the thrower ceases to move it; but because of the resistance of the air and the gravity of the stone, which inclines it to move in a direction opposite to that towards which the impetus tends to move it, this impetus is continually weakened. Therefore the movement of the stone will become continually slower, and at length, the impetus is so diminished or destroyed that the gravity of the stone prevails over it and moves the stone down towards its natural place. A. C. Crombie, Medieval and Early Modern Science </> This theory is sometimes called the Animistic theory of motion since it envisions a "life force" being associated with motion. Newton's 1st law is often very difficult to grasp because it contradicts various common-sense ideas of motion that they have acquired from experinece in everyday life. For example, unnaccounted for forces like friction might cause a ball rolling on the playground to eventually stop, even though no obvious forces seem to be acting. When studying Newtonian mechanics, it is best to remember this as two laws: 1. If the net force (i.e., sum of all forces) acting on an object is zero, the object will keep moving with constant velocity (which may be zero). 2. If an object is moving with constant velocity (not speed), that is, with zero acceleration, then the net force acting on that object must be zero.

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ch04-newtons-law-of-motion - MasteringPhysics Assignment...

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