1 / 65

Acceleration

This text explains the concepts of acceleration and velocity, including constant acceleration, acceleration of gravity, and velocity-time graphs. It also provides equations and examples to calculate average and uniform acceleration and displacement.

twoodard
Download Presentation

Acceleration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Acceleration

  2. Velocity vs. Acceleration Velocity (v) - rate of position change. Constant v – rate stays the same, equal distance for equal t interval. Acceleration (a)- rate of velocity change. Constant/Uniform accl. – change v for equal time interval. To calculate average/ uniform / constant accl a = Dv a = vf – vi t t

  3. Acceleration • Any object not traveling at constant velocity is accelerating. • Changing speed – either speeding up or slowing down. • Changing direction.

  4. We will look at Uniform / Constant Acceleration Changing speed or direction at constant rate. What are units?

  5. Since a = Dv /tUnits become: m Dv s = m or d/t2. t s s2 What does it mean to have a constant or uniform acceleration of = 10 m/s2.

  6. Acceleration of Gravity (g) near the surface of the Earth. • ~ 10 m/s2. • Drop a ball from rest (vi = 0) • After 1 sec, it’s velocity ~ 10 m/s • After 2 sec, it’s velocity ~

  7. a. If I drop a ball from rest near Earth’s surface, approximately how fast is it moving after falling 5 seconds? • 50 m/s

  8. Acceleration is a vector.Magnitude & direction.When Dv is positive accl is positivesince Dv tWhat does the sign of accl mean?

  9. Sign of acceleration Sign tells change in v. 1. Consider a car starts from rest, heads east, and attains a velocity of +20 m/s in 2 s. Calculate a:

  10. a = vf –vi t a = Dv +20 m/s - 0 m/s = +10 m/s2t 2 s Acceleration is positive. The car is headed in a positive direction and speeding up. 2. Now consider the same car slowing to a stop from +20 m/s in 2s. Calculate a.

  11. Now vf is 0, and vi is +20m/s, so.a = Dv 0 m/s - (+20 m/s) = -10 m/s2. Dt 2s Accl is neg. the car is slowing down. Hold on - its not so simple! 3. Consider the same car starts from rest, heads west, and reaches 20 m/s in 2 s. Calculate a now. Since the car is heading west, the vf is neg.

  12. A quick calculation shows this new accl to be negative. Oy!Here are the rules:

  13. Velocity motion a pos speeding +pos slowing -neg speeding -neg slowing + Mental Trick!

  14. 4. A shuttle bus slows to a stop with an acceleration of -1.8 m/s2. How long does it take to slow from 9.0 m/s to rest? • List the variables. • a = -1.8 m/s2. • vi = 9 m/s • vf = 0 (stop) • t = ?

  15. a = -1.8 m/s2. • vi = 9 m/s • vf = 0 (stop) • t = ? • Find an equation with everything on the list. • a = vf– vi/t • Rearrange to solve for the unknown. • t = vf– vi/a • Plug in with units. • = 9m/s – 0 = 5 s. -1.8 m/s2

  16. 5. A plane starts from rest and accelerates for 6 minutes at 20 m/s2 before traveling at a constant velocity. What was its final velocity? • 7200 m/s.

  17. Another useful acceleration equation. • d = vit + ½ at2. • d= displacement (m) • vi = initial (starting velocity) m/s. • a = acceleration m/s2. • t = time over which accl takes place - s.

  18. 6. A car starts from rest and accelerates at 5 m/s2 for 8 seconds. How far did it go in that time? • List! • Equation! • Solve. • 160 m

  19. Acceleration Hwk. • Hwk Intro to Acceleration Rd 48 – 49 Do pg 49 #1 - 5.

  20. 1. Take your seat. • 2. Take out your physics supplies. • 3. Will 6 volunteers come to the front please

  21. Do Now: • Ruler Drop.

  22. More Acceleration Equations • a = Dv/t • vf = vi + at • d = vit + ½ at2. • vf2 = vi2 + 2 ad.

  23. 1. A car starts from rest and accelerates at 6 m/s2 for 5 seconds. How far did it travel?

  24. 2. A car slows to a stop from 23 m/s by applying the brakes over 12 meters. Calculate acceleration. • vi = 23 m/s • vf = 0 • d = 23 m • a = ? • vf2 = vi2 + 2ad • - vi2 = a • 2d • -(23 m/s)2= -22 m/s2. 2(12m)

  25. 3.A bicycle is traveling at 5 m/s. It accelerates at 3 m/s2 for 3 meters. What is its final velocity?

  26. 4. A truck skidded to a stop with an acceleration of -3 m/s2. If its initial velocity was 11 m/s, how far was it skidding before it came to a stop?

  27. Hwk Wksht Mixed Accl Equations sheet.

  28. Velocity Time GraphsSpeed Time Graphs

  29. Constant Velocity/Speed

  30. Constant / Uniform Acceleration. On velocity time graph accl. is slope of straight line.

  31. What’s going on here?

  32. Sign of velocity is direction.

  33. Sketch Graphs V-t sketch graphs Rev BookHwk Rev Book. Rd 55 – 58. Do pg 56 #7-13 AND Pg 58 #14 – 18.

  34. Displacement on V-T graphs

  35. Displacement = Area Under Curvev = d/t then, vt = d.

  36. Area of non-constant velocity. For constant accl, d = area of a triangle: ½ bh.If a car achieved a v=40 m/s in 10 s, then:½(10s)(40m/s) = 200 m. 40 m/s 10 s

  37. To find displacement, calc area of triangle + rectangle.

  38. How can you tell when object is back to starting point? • Positive displacement = negative displacement.

  39. Do Now: Given the v – t graph below, sketch the acceleration – t graph for the same motion.

  40. Acceleration – time Graphs • What is the physical behavior of the object? • Slowing down pos direction, constant vel neg accel.

  41. d-t: • slope = velocity • area ≠ . • v-t: • slope = accl • area = displ • a-t: • slope ≠ . • area = D vel • vf – vi.

  42. Hwk Rev Book pg 76 #32-36, 45-47, 49 – 55, 59-60. Begin in class.

  43. Together: text pg 65 #1-5,pg 72 # 34, 35, 48, 49. Test Thursday: Acceleration, Motion Graphs, Free-fall. Text 2-2, 2-3. RB Chap 3.

  44. Objects Falling Under Gravity

  45. Freefall Gravity accelerates uniformly masses as they fall and rise. Earth’s acceleration rate is 9.81 m/s2 – very close to 10 m/s2.

  46. Falling objects accelerate at the same rate in absence of air resistance

  47. But with air resistance

  48. Fortunately there is a “terminal fall velocity.” After a while, the diver falls with constant velocity due to air resistance. Unfortunately terminal fall velocity is too large to live through the drop.

More Related