ism_chapter_04

ism_chapter_04 - Chapter 4 Newton's Laws Conceptual...

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195 Chapter 4 Newton’s Laws Conceptual Problems *1 •• Determine the Concept A reference frame in which the law of inertia holds is called an inertial reference frame. If an object with no net force acting on it is at rest or is moving with a constant speed in a straight line (i.e., with constant velocity) relative to the reference frame, then the reference frame is an inertial reference frame. Consider sitting at rest in an accelerating train or plane. The train or plane is not an inertial reference frame even though you are at rest relative to it. In an inertial frame, a dropped ball lands at your feet. You are in a noninertial frame when the driver of the car in which you are riding steps on the gas and you are pushed back into your seat. 2 •• Determine the Concept A reference frame in which the law of inertia holds is called an inertial reference frame. A reference frame with acceleration a relative to the initial frame, and with any velocity relative to the initial frame, is inertial. 3 Determine the Concept No. If the net force acting on an object is zero, its acceleration is zero. The only conclusion one can draw is that the net force acting on the object is zero. * 4 Determine the Concept An object accelerates when a net force acts on it. The fact that an object is accelerating tells us nothing about its velocity other than that it is always changing. Yes, the object must have an acceleration relative to the inertial frame of reference. According to Newton’s 1 st and 2 nd laws, an object must accelerate, relative to any inertial reference frame, in the direction of the net force. If there is only a single nonzero force, then this force is the net force. Yes, the object’s velocity may be momentarily zero. During the period in which the force is acting, the object may be momentarily at rest, but its velocity cannot remain zero because it must continue to accelerate. Thus, its velocity is always changing. 5 Determine the Concept No. Predicting the direction of the subsequent motion correctly requires knowledge of the initial velocity as well as the acceleration. While the acceleration can be obtained from the net force through Newton’s 2 nd law, the velocity can only be obtained by integrating the acceleration. 6 Determine the Concept An object in an inertial reference frame accelerates if there is a net force acting on it. Because the object is moving at constant velocity, the net force acting on it is zero. correct. is ) ( c

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Chapter 4 196 7 Determine the Concept The mass of an object is an intrinsic property of the object whereas the weight of an object depends directly on the local gravitational field. Therefore, the mass of the object would not change and local grav mg w = . Note that if the gravitational field is zero then the gravitational force is also zero.
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This homework help was uploaded on 02/26/2008 for the course PHYSICS 11 taught by Professor Licini during the Spring '07 term at Lehigh University .

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ism_chapter_04 - Chapter 4 Newton's Laws Conceptual...

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