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Unformatted text preview: 1 CHAPTER 2 Describing Motion: Kinematics in One Dimension Introduction The study of motion of objects, and the related concepts of force and energy, for the field called mechanics. Mechanics is divided into two parts: ! kinematics , which is the description of how objects move ! dynamics , which deals with force and why objects move as they do. Reference Frames and Displacement Any measurement of position, distance, or speed, must be made with respect to a frame of reference . In physics, we often draw a set of coordinate axes to represent a frame of reference. A person walks toward the front of a train at 5 km/h. The train is moving 80 km/h with respect to the ground, so the walking persons speed, relative to the ground is 85 km/h. Displacement We need to make a distinction between the distance an object has traveled and its displacement , which is defined as the change in position of the object. Distance is a scalar quantity. Displacement is a vector quantity that has both magnitude and direction. A person walks 70 m east and then 30 m west. The total distance traveled is 100 m, but the displacement is 40 m to the east. Displacement We need to make a distinction between the distance an object has traveled and its displacement , which is defined as the change in position of the object. Distance is a scalar quantity. Displacement is a vector quantity that has both magnitude and direction. A person walks 70 m east and then 30 m west. The total distance traveled is 100 m, but the displacement is 40 m to the east. Example: A particle move along a circular path from A back to A. Calculate the total distance and displacement Distance = 2 R Displacement = r = (r finalr initial ) = 0 R R = radius A Initial and final point are the same Average Speed The average speed of an object is defined as the total distance traveled along its path divided by the time it takes to travel this distance : average speed = = d/ ! t distance traveled time elapsed Average Velocity Speed is simple a positive number, with units. Velocity is used to signify both the magnitude (numerical value) of how far an object is moving and the direction in which it is moving. Average velocity = = ! r/ ! t displacement time elapsed final position initial position Time elapsed 7 Instantaneous Velocity The instantaneous velocity at any moment is defined as the average velocity over an infinitesimally short time interval ....
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This note was uploaded on 04/23/2011 for the course JAPAN 7b taught by Professor Wallace during the Spring '11 term at University of California, Berkeley.
 Spring '11
 wallace

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