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PHY183-Lecture05p

# PHY183-Lecture05p - Clicker Quiz Physics for Scientists...

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1 January 17, 2012 Physics for Scientists&Engineers 1 1 Physics for Scientists & Engineers 1 Fall Semester 2011 Lecture 5 Position, Displacement, Speed, Velocity Clicker Quiz January 17, 2012 Physics for Scientists&Engineers 1 2 The train in this picture is A. Slowing down B. Speeding up C. Moving at a constant speed D. Can’t tell Kinematics Mechanics is the study of motion and its causes Mechanics is the main focus of this course Kinematics is the study of the motion of objects For now We will not worry about what causes the motion We will concentrate on translational motion The motion of the point location of the center of mass of objects We will not worry about rotation We define the position of an object with is position vector January 17, 2012 Physics for Scientists&Engineers 1 3 r January 17, 2012 Physics for Scientists&Engineers 1 4 Position Vectors for one-dimensional motion have only one component, x -component for now Use the symbol x to denote position vector Note: we leave the vector arrows off for 1d vectors All position vectors are measured relative to the origin of the coordinate system, which can be chosen arbitrarily Vector x can be positive or negative (its magnitude is again always positive, though) Examples for proper 1d position vectors (SI-unit m , + or -) Position vector is a function of time Notation for the time-dependent position vector: x ( t ) Notation: Vector x at some specific time t 1 : x ( t 1 ) =x 1 7 16 0.73 m, 4' 3 ", 13.6 km x x x = = = − January 17, 2012 Physics for Scientists&Engineers 1 5 Graphical Representation Example: Car is driving down the road (top view) As the car passes the blue dot, we start our clock and record its position in regular time intervals Case 1: constant speed Case 2: speeding up Case 3: coming to a halt January 17, 2012 Physics for Scientists&Engineers 1 6 Graphs of the Position Vector We can dispense with the car and simply record the location of its center, obtaining a graph of position vector vs. time Typical of motion with constant velocity

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