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Chapter 2

Chapter 2 . Section 2 Acceleration. Objectives. Students will learned about Describing acceleration Apply kinematic equations to calculate distance, time , or velocity under conditions of constant acceleration. Acceleration .

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Chapter 2

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  1. Chapter 2 Section 2 Acceleration

  2. Objectives • Students will learned about • Describing acceleration • Apply kinematic equations to calculate distance, time , or velocity under conditions of constant acceleration.

  3. Acceleration • What is acceleration?Answer: Is the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change.

  4. acceleration • Acceleration has direction and magnitude. Thus, acceleration is a vector quantity. • The units of acceleration are meters per second squared.

  5. Acceleration problem • Problem #1 • A shuttle bus slows down with an average acceleration of -1.8 . How long dos it take the bus to slow from 9 m/s to complete stop.

  6. Example 2 • A skater increases her velocity from 2 m/s to 10 m/s in 30 seconds. What is the skater’s acceleration?

  7. Example 3 • A car accelerates at a rate of 3 . If the original speed is 8 m/s, how many seconds will it take the car to reach a final speed of 25 m/s?

  8. Student Guided Practice Do problems from worksheet 1 ,2 and4

  9. Changes in velocity • Imagine that a train is moving to the right so that the displacement and the velocity are positive. • The velocity increases in magnitude as the train picks up speed, the final velocity will be greater than the initial velocity. So, the average velocity( will be positive and the acceleration is positive. • When the velocity is constant the acceleration is zero. • When a train slows down, the velocity still positive but the initial velocity is greater than the final velocity , so the average velocity is negative as well as the acceleration.

  10. Changes in velocity • The slope of the velocity-time graph is the averageacceleration. • When the velocity in the positive direction is increasing, the acceleration is positive, as at A. • When the velocity is constant, there is no acceleration, as at B. • When the velocity in the positive direction is decreasing, the acceleration is negative, as at C.

  11. Signs

  12. Motion with constant speed • When velocity changes by the same amount during each time interval,acceleration is constant. • The relationships betweendisplacement, time,velocity,andconstant accelerationare expressed by the equations shown on the next slide. These equations apply to any object moving with constant acceleration. • These equations use the following symbols: x = displacement vi = initial velocity vf= final velocity t = time interval

  13. Equations

  14. Displacement with constant acceleration • A racing car reaches a speed of 42 m/s. If then begins a uniform negative acceleration, using its parachute and braking system, and comes to rest 5.5 seconds later. Find the distance that the car travels during braking.

  15. Example #2 • A car accelerates uniformly from rest to a speed of 6.6 m/s in 6.5 s. Find the distance the car travels during this time.

  16. Student guided practice • Do problems 2-4 from page 49

  17. Velocity and displacement with constant acceleration • A plane starting at rest at one end of the runway undergoes a uniform acceleration of 4.8 for 15 seconds before takeout. What is the speed of the takeout? How long must the runway be for the plane to be able to take off?

  18. Example 1 • A car with initial speed of 6.5 m/s accelerates at a uniform rate of .92 for 3.6 s. find the final speed and the displacement of the car during this time.

  19. Student guided practice • Do 2-4 page 51

  20. Final velocity after any displacement Final Velocity After Any Displacement A person pushing a stroller starts from rest, uniformly accelerating at a rate of 0.500 m/s2. What is the velocity of the stroller after it has traveled 4.75 m?

  21. Homework • Do problems from student practice • Problems 1-6 from page 54

  22. Closure • Today we saw about acceleration and how we can find it. • Next class we are going to continue with falling objects.

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