# Lecture08 - PHYSICS 149 Lecture 8 Chapter 3 3.1 Position and Displacement 3.2 Velocity and Acceleration Lecture 8 Purdue University Physics 149 1

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PHYSICS 149: Lecture 8 • Chapter 3 – 3.1 Position and Displacement – 3.2 Velocity and Acceleration Lecture 8 Purdue University, Physics 149 1

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ILQ 1 Find W 2 ? A) W sin θ B) W cos θ C) N sin θ D) N cos θ T W N W 2 NOTE: because of ideal pulley and cord W 2 = T θ Lecture 8 2 Purdue University, Physics 149
Lecture 8 Purdue University, Physics 149 3 +x -x 0 The variables are time and distance t = 0 start of observations at a point x 0 t = t end of the observations at a point x f All quantities except time are vectors but the vector nature is contained in whether the quantity is positive or negative Motion in One Dimension Objects are in motion and velocity is (change in distance)/time Velocity can change => acceleration (change in velocity)/time

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Position Vector • To describe position, we need – a reference point (origin), – a distance from the origin, and – a direction from the origin. • Position Vector (or Position) – A vector quantity that consists of the distance and direction – An arrow starting at the “origin” and ending with the arrowhead on the object – Position vector is usually denoted by r . • The x-, y-, and z- component of r are usually written simply as x , y , and z (instead of r x , r y , and r z ). object at ( x,y ) Lecture 8 4 Purdue University, Physics 149
Lecture 8 Purdue University, Physics 149 5 Position • A vector quantity describing where you are relative to an origin – Point A is located at x=3, y=1 or (3,1) – Point B is located at (-1,-2) • The vector r A indicating the position of A starts at the origin and terminates with arrowhead A • Same for r B and B y x 3 3 -3 -3 A B

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Distance vs. Displacement Lecture 8 Purdue University, Physics 149 6 • Distance (scalar) – Total length of path traveled – The path of an object does matter • Displacement (vector) – The change of the position vector ( r ), that is, the final position vector ( r f ) minus the initial position vector ( r i ) = r f + (– r i ) – An arrow starting at the initial position (the tip of the initial position vector) and ending with the arrowhead at the final position (the tip of the final position vector) – The path of an object does not matter. The displacement depends only on the starting and ending points.
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## This note was uploaded on 04/23/2011 for the course PHYS 149 taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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Lecture08 - PHYSICS 149 Lecture 8 Chapter 3 3.1 Position and Displacement 3.2 Velocity and Acceleration Lecture 8 Purdue University Physics 149 1

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