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# Acceleration

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1. Acceleration Section 2.2

2. Standards Covered • PS – 5.3 Explain how changes in velocity and time affect the acceleration of an object • PS – 5.4 Use the formula a = (vf-vi)/t to determine the acceleration of an object

3. Acceleration • Acceleration – rate of change of velocity • Object changes its speed, direction, or both • Positive acceleration – object is speeding up • Negative acceleration – object is slowing down

4. Calculating Acceleration • Acceleration = change in velocity time = vfinal – vinitial = vf – vi time t • Units = m/s – m/s = m/s2 s

5. Example #1 • Suppose a jet airliner starts at rest at the end of runway and reaches a speed of 80 m/s in 20 s. What is its acceleration? a= vf – vi t = 80 – 0 20 = 4 m/s2

6. Example #2 • A skateboarder is moving at a speed of 3 m/s and comes to a stop in 2s. Calculate the acceleration of the skateboarder. a= vf – vi t = 0 – 3 2 = -1.5 m/s2

7. Your Turn!! • A car accelerates from a standstill to 60 km/s in 10.0 seconds. What is its acceleration? • A car accelerates from 25 km/s to 55 km/s in 30 seconds. What is its acceleration? • A runner achieves a velocity of 11.1 m/s, 9 seconds after he begins. What is his acceleration?

8. Graphing Acceleration • Velocity goes on the y-axis • Time goes on the x-axis • Slope = rise(y) = velocity = acceleration run(x) time • Upward slope – (+) acceleration – speeding up • Downward slope – (-) acceleration – slowing down • Flat line – 0 acceleration – constant speed