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Physics 31

Physics 31. Friday August 29. Our Class. Major 17 Bio, 1 Eng, 1 Psychology HS Physics 11/19 yes Calculus I or higher, taken or taking 14/19 22 Lab 14 yes MCAT or PCAT 5 yes EXCEL 16 yes. What is the difference between speed and velocity?

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Physics 31

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  1. Physics 31 Friday August 29

  2. Our Class Major 17 Bio, 1 Eng, 1 Psychology HS Physics 11/19 yes Calculus I or higher, taken or taking 14/19 22 Lab 14 yes MCAT or PCAT 5 yes EXCEL 16 yes

  3. What is the difference between speed and velocity? • Speed is an average quantity, while velocity is not. • 2. Velocity contains information about the direction of motion while speed does not. • 3. Speed is measured in mph, while velocity is measured in m/s. • 4. The concept of speed applies only to objects that are neither speeding up nor slowing down, while velocity applies to every kind of motion. • 5. Speed is used to measure how fast an object is moving in a straight line, while velocity is used for objects moving along curved paths.

  4. The quantity 2.67 x 103 m/s has how many significant figures? • 1 • 2 • 3 • 4 • 5

  5. If Sam walks 100 m to the right, then 200 m to the left, his net displacement vector points • To the right • To the left • Has zero length • Cannot tell without further information

  6. Vectors and Motion A quantity that requires both a magnitude (or size) and a direction can be represented by a vector. Graphically, we represent a vector by an arrow. The velocity of this car is 100 m/s (magnitude) to the left (direction). This boy pushes on his friend with a force of 25 N to the right. Slide 1-28

  7. Displacement Vectors A displacement vector starts at an object’s initial position and ends at its final position. It doesn’t matter what the object did in between these two positions. In motion diagrams, the displacement vectors span successive particle positions. Slide 1-29

  8. QUIZ #1 • Alice is sliding along a smooth, icy road on her sled when she suddenly runs headfirst into a large, very soft snow bank that gradually brings her to a halt. Draw a motion diagram for Alice. Show and label all displacement vectors. • Make a plot of her velocity vs. time. Plot same times as in part 1. • Name on paper

  9. Adding Displacement Vectors Slide 1-31

  10. Example: Adding Displacement Vectors • Jenny runs 1 mi to the northeast, then 1 mi south. Graphically find her net displacement.

  11. N E W S

  12. Adding Vectors Graphically Slide 1-33

  13. Velocity Vectors Slide 1-34

  14. Example: Velocity Vectors Jake throws a ball at a 60° angle, measured from the horizontal. The ball is caught by Jim. Draw a motion diagram of the ball with velocity vectors. Slide 1-35

  15. Adding velocity vectors • add red vector to initial velocity to get next velocity vector and so on…..

  16. Homework for today • Problems Ch. 1: MC24, MC28, 9, 10, 25, 36, 37, 38, WB 1.6(27,28)

  17. Homework for Monday • NO ClassLABOR DAY

  18. Homework for Wednesday • Reading: 2:1-2-Motion in One Dimension-Constant Velocity • Problems: 1: 28, 30, 32, 35, 43, 47, 51, 56

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