18 ∆v ∆v = vf - vi The ∆ means the change in… So ∆v means change in velocityYou find the change in a value by subtracting it initial value from its final value∆v = final velocity – initial velocity∆v = vf vi18
19 Final Equation for average/overall acceleration a = (vf - vi) / tvf = final velocityvi = initial velocityt = elapsed timea = acceleration19
20 Ex #1A flowerpot falls off a second story windowsill. The flowerpot start from rest and hits the sidewalk 1.5 s later with a velocity of 14.7m/s. Find the average acceleration.20
21 What information is given? Identify the information. Is the time14.7 m/sis the final velocityStarts from restMeans that the initial velocity is zero (0)“at rest” always means that vi = o21
22 Answer #1 a = (14.7 – 0) / 1.5 = 9.8 What are the units? (14.7 m/s – 0 m/s) 1.5 s = (m/s) / sm / s222
24 Constant acceleration Occurs when rate of change in the velocity of an object is constant.This means the velocity values change at the same rate each secondAn object that accelerates at 3 m/s2, goes from rest (0 m/s) to:3 m/s after 1 second, 6 m/s after 2 sec,9 m/s after 3 sec…24
25 Constant acceleration and the graphs Constant acceleration is indicated by a smooth curve on a P-t graph, and a straight line on a V-t graph.Slope of the line on a V-t graph = value of constant acceleration
26 Ex What is the acceleration of the object at 5 min? What is the acceleration of the object at any time between 15 min and 40 min?
27 Constant Acceleration An object moving at a constant velocity has a constant acceleration of zeroAs evidenced in a graph by a straight horizontal line27
28 Positive acceleration Positive slope of V-t graph, graph gets higher moving left to rightGetting faster in the positive directionGetting slower in the negative direction28
29 Negative acceleration Graph gets lower moving left to rightSlowing down in the positive directionSpeeding up in the negative direction29
30 QuestionWhat is the difference between constant velocity and constant acceleration?30
31 AnswerConstant velocity means the object does not change its velocity over timeConstant acceleration means that the object does not change its acceleration over time
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