# Ch. 2.pdf - Chapter 2 Kinematics-1D Position x(in meters...

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Chapter 2 Kinematics-1D Position, x (in meters) changes with Time t (in seconds)

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Reference Frames Any measurement of position, distance, or speed must be made with respect to a reference. Will use + and signs to indicate positions in front or in back of the reference point Position-Time Graph ---- shows the motion of the particle (car)
Distance and displacement Distance: the length of a path followed by a particle, always positive. Displacement: change in position during some time interval Δ x = x 2 – x 1 Can be positive and negative We make a distinction between distance and displacement.

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Average Velocity and Speed The average velocity is rate at which the displacement occurs The average speed = total distance / total time is a scalar quantity, always positive The SI unit of velocity and speed is m/s v average = Δ x Δ t = x f x i Δ t
Simple practice What are the average velocity and speed in the first 40 s?

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Example The position versus time for a certain particle moving along the x axis is shown in Figure. Find the average velocity and speed in the time intervals (a) 0 to 2 s, (b) 0 to 4 s, and (c) 0 s to 8 s.
A person walks first at a constant speed of 6.00 m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 3.00 m/s. What is (a) her average velocity over the entire trip? (b) her average speed over the entire trip?

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Instantaneous Velocity The limit of the average velocity as the time interval becomes infinitesimally short, or as the time interval approaches zero.
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