chapter5

chapter5 - Chapter 5 The Laws of Motion The Laws of Motion...

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Chapter 5 The Laws of Motion

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The Laws of Motion The description of an object in motion included its position, velocity, and acceleration. There was no consideration of what might influence that motion. Two main factors need to be addressed to answer questions about why the motion of an object will change. ± Forces acting on the object ± The mass of the object Dynamics studies the causes of motion. Will start with three basic laws of motion ± Formulated by Sir Isaac Newton Introduction
Sir Isaac Newton 1642 ± 1727 Formulated basic laws of mechanics Discovered Law of Universal Gravitation Invented form of calculus Many observations dealing with light and optics Section 5.1

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Force Forces in everyday experience ± Push on an object to move it ± Throw or kick a ball ± May push on an object and not be able to move it Forces are what cause any change in the velocity of an object. ± Newton±s definition ± A force is that which causes an acceleration Section 5.1
Classes of Forces Contact forces involve physical contact between two objects ± Examples a, b, c Field forces act through empty space ± No physical contact is required ± Examples d, e, f Section 5.1

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Fundamental Forces Gravitational force ± Between objects Electromagnetic forces ± Between electric charges Nuclear force ± Between subatomic particles Weak forces ± Arise in certain radioactive decay processes Note: These are all field forces. Section 5.1
More About Forces A spring can be used to calibrate the magnitude of a force. Doubling the force causes double the reading on the spring. When both forces are applied, the reading is three times the initial reading. Section 5.1

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Vector Nature of Forces The forces are applied perpendicularly to each other. The resultant (or net) force is the hypotenuse. Forces are vectors, so you must use the rules for vector addition to find the net force acting on an object. Section 5.1
Newton±s First Law If an object does not interact with other objects, it is possible to identify a reference frame in which the object has zero acceleration. ± This is also called the law of inertia. ± It defines a special set of reference frames called inertial frames. ± We call this an inertial frame of reference. Section 5.2

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Inertial Frames Any reference frame that moves with constant velocity relative to an inertial frame is itself an inertial frame. If you accelerate relative to an object in an inertial frame, you are observing the object from a non-inertial reference frame. A reference frame that moves with constant velocity relative to the distant stars is the best approximation of an inertial frame. ± We can consider the Earth to be such an inertial frame, although it has a small centripetal acceleration associated with its motion.
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This note was uploaded on 02/15/2011 for the course PHYS 111 taught by Professor Moro during the Spring '08 term at NJIT.

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chapter5 - Chapter 5 The Laws of Motion The Laws of Motion...

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