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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 person’s 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 π R Displacement = Δ 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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 Spring '11
 wallace
 Acceleration, Velocity, HRW, 8.00 m, 5 km/h, 2 1

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