Lecture09

Lecture09 - PHYSICS 149 Lecture 9 Chapter 3 3.2 Velocity...

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PHYSICS 149: Lecture 9 • Chapter 3 – 3.2 Velocity and Acceleration – 3.3 Newton’s Second Law of Motion – 3.4 Applying Newton’s Second Law – 3.5 Relative Velocity Lecture 9 Purdue University, Physics 149 1
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Lecture 9 Purdue University, Physics 149 2 t x(t) Δ t Δ x x(t) t Velocity (m/s) • The average velocity is the change in position (vector) divided by the change in time. • Instantaneous velocity is the limit of average velocity as t gets small. It is the slope of the x(t) plot.
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Lecture 9 Purdue University, Physics 149 3 If the average velocity of a car during a trip along a straight road is positive, is it possible for the instantaneous velocity at some time during the trip to be negative? A - Yes B - No correct If the car is traveling in a straight path the velocity will always be positive. The car needs to travel in the opposite direction to get a negative velocity . The car might have reversed for a little while along the trip creating a negative instantaneous velocity at the point. If the overall displacement of the car is positive for that particular time interval, than the average velocity is positive as well. ILQ 1
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Lecture 9 Purdue University, Physics 149 4 How to determine x from v(t) • The total displacement x during and time t is the area under the graph v(t) • Assume 1D, and v constant: t v Δ x v 1x t 1 t 2
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Lecture 9 Purdue University, Physics 149 5 • The average acceleration is the change in velocity divided by the change in time. • Instantaneous acceleration is limit of average acceleration as t gets small. It is the slope of the v(t) plot. t v(t) Δ t Δ v v(t) t Acceleration (m/s 2 )
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Average Acceleration • Average acceleration is the change in velocity during the time interval during which the velocity changed. • The x- and y-components of the average velocity are: • Typical units for the magnitude of acceleration are m/s 2 , km/s 2 , and so on. Lecture 9 6 Purdue University, Physics 149
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Instantaneous Acceleration • Instantaneous acceleration is the average acceleration we measure when the time interval is infinitesimally short. • The x- and y-components of the instantaneous velocity are: Lecture 9 7 Purdue University, Physics 149
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Direction of Acceleration • If speed is increasing , v and a are in same direction. • If speed is decreasing , v and a are in opposite direction. Lecture 9 8 Purdue University, Physics 149
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• A go-kart travels around a circular track at a constant speed. Which of these is a true statement? (a) The go-kart has a constant velocity. (b) The go-kart has zero acceleration.
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Lecture09 - PHYSICS 149 Lecture 9 Chapter 3 3.2 Velocity...

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