Chapter 11 Motion

1. Chapter 11Motion 11.3 Acceleration

2. What Is Acceleration? How are changes in velocity described? The rate at which velocity changes is called acceleration.

3. What Is Acceleration? • Acceleration applies to any change in an object’s velocity. • positive acceleration - increasing change in speed • negative acceleration - decreasing change in speed. Also called Deceleration

4. What Is Acceleration? Free fall is the movement of an object toward Earth solely because of gravity. • The unit for velocity = meters per second. • The unit for acceleration = meters per second squared (m/s2). Objects falling near Earth’s surface accelerate downward at a rate of 9.8 m/s2.

5. What Is Acceleration? t = 0 sv = 0 m/s Each second an object is in free fall, its velocity increases downward by 9.8 meters per second. The change in the stone’s speed is 9.8 m/s2, the acceleration due to gravity. t = 1 sv = 9.8 m/s t = 2 sv = 19.6 m/s t = 3 sv = 29.4 m/s

6. What Is Acceleration? The velocity of an object moving in a straight line changes at a constant rate when the object is experiencing constant acceleration. • Constant accelerationis a steady change in velocity.

7. Acceleration is the rate at which velocity changes. Viis the initial velocity, vfis the final velocity, and t is total time.

8. Calculating Acceleration Calculating Acceleration A ball rolls down a ramp, starting from rest. After 2 seconds, its velocity is 6 meters per second. What is the acceleration of the ball?

9. 1.A car traveling at 10 m/s starts to decelerate steadily. It comes to a complete stop in 20 seconds. What is its acceleration?

10. 2. An airplane travels down a runway for 4.0 seconds with an acceleration of 9.0 m/s2. What is its change in velocity during this time?

11. Describing Ionic Compounds 3. A child drops a ball from a bridge. The ball strikes the water under the bridge 2.0 seconds later. What is the velocity of the ball when it strikes the water?

12. 4. A boy throws a rock straight up into the air. It reaches the highest point of its flight after 2.5 seconds. How fast was the rock going when it left the boy’s hand?

13. Acceleration Example • A flowerpot falls off a second story windowsill. It starts from rest and hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. Find the average acceleration of the flowerpot.

14. Acceleration Practice • A skateboard accelerates from 0 m/s to 4 m/s in 2.5 s. • A swimming turtle has a speed of 0.50 m/s. After 4 s, its speed is 0.80 m/s. • A train slows down from 12 m/s to 9.6 m/s in 0.8 s.

15. Graphs of Accelerated Motion How does a speed-time graph indicate acceleration? The slope of a speed-time graph is acceleration.

16. Graphs of Accelerated Motion Speed-Time Graphs Constant acceleration is represented on a speed–time graph by a straight line. The slope of the line is the acceleration.

17. Graphs of Accelerated Motion Distance-Time Graphs Accelerated motion is represented by a curved line on a distance-time graph.

18. Speed-Time Graph Graphing Acceleration Specify the time period when the object was... • slowing down • speeding up • moving at a constant speed • not moving

19. Acceleration Problem • Timothy was playing ball in the house when his ball bounced out the window. A freely falling object accelerates at 9.8 m/s/s. What is the velocity of Timothy’s ball after 2 s?

20. Instantaneous Acceleration Instantaneous acceleration is how fast a velocity is changing at a specific instant.

21. Assessment Questions • What is acceleration? • the rate at which speed increases • the time an object’s velocity increases • the rate at which displacement changes • the rate at which velocity changes

22. Assessment Questions • A sports car can accelerate from 0 m/s to 28 m/s in four seconds. What is the acceleration of the car? • 24 s • 7 m/s • 27 m/s • 14 m/s

23. Assessment Questions • If you were to sketch a displacement-time graph and a speed-time graph for an object experiencing constant acceleration, what would they look like? • Both graphs would be linear, with the displacement-time graph being steeper. • Both graphs would be linear, with the speed-time graph being steeper. • Both graphs would be nonlinear. • The speed-time graph would be linear; the displacement-time graph would be nonlinear.

24. Assessment Questions • Which of the following is an example of negative acceleration? • Mike starts riding his bike and uses the pedals to go from 0 km/h to 20 km/h. • Mike pedals up a hill and gradually slows from 20 km/h to 5 km/h. • Mike sits on his bike at the top of the hill and rests. • Mike coasts downhill without pedalling, going from 0 km/h to 15 km/h.

25. Assessment Questions • The acceleration at a specific point on a distance-time graph is the • instantaneous acceleration. • momentary acceleration. • positive acceleration. • numerical acceleration.

26. Assessment Questions 6. If an object experiences a steady velocity change in a straight line, it is undergoing constant acceleration.TrueFalse