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Linear Motion

Linear Motion. Mr. Callan Physics Assignment Read Chapter 2 Do all even questions on pages 25-27 (except activities) chapter review. “Do problems 1-8 in “Problem-Solving” work book on pages 1-14 (WB 1-14). Equations. Quiz How Fast are You Moving When You Are Sitting Still?.

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Linear Motion

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  1. Linear Motion Mr. Callan Physics Assignment Read Chapter 2 Do all even questions on pages 25-27 (except activities) chapter review. “Do problems 1-8 in “Problem-Solving” work book on pages 1-14 (WB 1-14)

  2. Equations

  3. QuizHow Fast are You Moving When You Are Sitting Still? • What is your observation? • What do you need to know?

  4. Hint 1 • At the equator the surface of the earth rotates around the center at about 1000 mph • At our latitude the movement is about 650 mph.

  5. Hint 2 • You are revolving around the sun at about 66 thousand miles per hour,

  6. Hint 3 • You are traveling around the center of the Milky Way galaxy at about 2 million miles per hour.

  7. Linear Motion • Motion in a straight line. 1 dimensional • Everything is in motion. • Motion is a rate. • Rate is a quantity divided by time. • Since everything moves, motion is relative not absolute. A space shuttle in orbit moves at about 8 km/sec. • But it also move very slow. • Review How fast is this in miles/hour?

  8. Speed • A measure of distance / time. • The rate could be mi/hr, km/sec, ft/sec etc. • Definition: Speed is the distance covered per unit of time. Per means “divided by.”

  9. Instantaneous Speed • A car does not move at one speed. It changes from zero to its maximum speed. • Your speedometer measures the cars instantaneous speed. • It is the speed at any one point in time.

  10. Average Speed • Average speed is used to plan trips. • It is the total distance traveled divided by the time it took to travel the distance. • Average Speed = total distance/time interval

  11. Velocity • Velocity and Speed are used interchangeably in everyday language. • But THEY ARE NOT THE SAME. • Velocity is speed in a given direction. • Such as 60 mile per hour North.

  12. Constant Velocity • No change in speed • No change in direction • Motion is a straight line

  13. Changing Velocity • Speed could be changing • OR • Direction could be changing. • OR Both

  14. Acceleration • The rate of change of velocity. • The change in velocity/time interval. • OR the rate of change of speed. • The change in speed/time interval. • deceleration is the acceleration in the negative direction.

  15. Additional Assignment • Always look at the questions in the yellow boxes.

  16. 2.5 Free Fall: How fast • An apple falls from a tree. Does it accelerate while falling? • What do we know? • It starts from rest (velocity and acceleration = 0) then gains speed. • The gain in speed indicates that the apple does indeed accelerate.

  17. Free Fall Cont. • Why does the apple accelerate? -Gravity • In this course we generally neglect air resistance (friction). • Therefore, we say that the apple is freely falling or is in free fall. • Objects in free fall increase their their velocity by about 10 m/s each second. • What does this mean?

  18. Free Fall • a =D v/ Dt = 10 m/s per sec. or 10 m/s/s • For objects in free fall a = g • More accurately g = 9.8 m/s2 • Since g = a = D v/ Dt • D v = g Dt for an object starting at rest the the initial velocity (vi) = zero, so the equation becomes v = g Dt . • If the initial time interval (ti) is set to zero, the the equation becomes v=gt

  19. Final Velocity with Initial Velocity • If someone throws a ball, it has an initial velocity. Vi = initial velocity • To calculate the final velocity Vf, the initial velocity is added into the equation. • Vf = g Dt + Vi • Lets say a ball is thrown straight down at 2m/s from the top of Sear Tower. How fast is it going after 3 seconds?

  20. 2.6 Free Fall: How far? • An object falling from rest is moving at 10 m/sec at one sec. But what is its average velocity? 10/2 • Time (sec) Instant Speed (m/s) Ave. Speed • 0 0 0 • 1 10 • 2 20 • 3 30 • 4 40

  21. Free Fall: How Far • The average velocity is the velocity we need for finding the distance. (vi+vf)/2=vave • d = 1/2 gt2 Look at the units! • meters=1/2 m/(sec x sec) x sec sec

  22. Free Fall: How far? • Time (sec) Instant Ave. Distance • 0 0 0 0 • 1 10 5 5 • 2 20 15 20 • 3 30 25 45 • 4 40 35 1/2gt2

  23. Reaction Time • A bill is 15.5 cm long so if your table mate places his/her thumb and finger over the center and you let go of the bill can your table mate catch the bill? • No, the bill falls 8 cm in 1/8 of a sec. Your reaction time is much greater.

  24. Let’s Measure your Reaction Time • Lab 2 • Find One and only one partner.

  25. Hang Time • Your hang time is related to how high you jump • d = ½ gt2 • Solve the vertical distance equation for time and then have your tablemate measure how high you can jump.

  26. Graph Matching

  27. 2.8 Air Resistance & Falling Objects • http://www.hq.nasa.gov/alsj/a15/a15v.1672206.mov

  28. Equations and Units • v=at, a=v/t, and t=a/v • v=gt, g=v/t and t = v/g • d=1/2at2 • Reaction time = (2d/a)1/2 , where a=g=9.8m/s2

  29. Chapter Review Due Thursday • Do the even problems on pages 25-27 • WB Wednesday • Test Friday

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