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Chapter 2 Notes

Chapter 2 Notes. Linear Motion. 2.1 Motion is Relative. Motion is all around us! (Cars on highway, trees in wind, stars & satellites, etc.) Motion is Relative- When we discuss the motion of something, we compare it’s motion relative to something else.

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Chapter 2 Notes

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  1. Chapter 2 Notes Linear Motion

  2. 2.1 Motion is Relative Motion is all around us! (Cars on highway, trees in wind, stars & satellites, etc.) • Motion is Relative- When we discuss the motion of something, we compare it’s motion relative to something else. (Shuttle moves 8 km/s relative to the earth)

  3. 2.2 Speed • Speed- Measure of how fast something is moving or the rate at which distance is covered. Possible Units: (mi/hr), (m/s), (km/h), (cm/day) → Instantaneous Speed: The speed at any instant. → Average Speed: Total distance covered ÷ Time interval S = d/t The speed which the speedometer reads at any given instant The average of all the speedometer readings

  4. Check Understanding: • If you ride your bike a distance of 5m in 1s, what is your speed? For 10m in 2s? B. If you drove 140 miles to Spokane, WA in 2 hours, how fast were you driving?

  5. 2.3 Velocity • Velocity- Speed in a given direction. E.g. Car moving 60 km/h to the north. →Constant Velocity- Constant speed and constant direction. →Changing Velocity- If the speed or direction (or both) is changing. • Controls that change velocity: gas pedal, brake, steering wheel.

  6. Check Understanding: • If the speedometer of a car moving northward reads 60km/h and it passes another car that travels southward at 60km/h. Do both cars have the same speed? Do they have the same velocity? B. If an airplane travels 500 km due north in 1 hr, what is its velocity? 250 km due north in ½ hr?

  7. 2.4 Acceleration • Acceleration- The rate at which the velocity is changing with respect to time. Units: time enters twice; once for unit of speed and again for interval of time which speed is changing. E.g. 10 m/s/s or 10m/s2 = Change in Motion or Change in Direction or Velocity

  8. Deceleration: (Negative acceleration) a decrease per second in speed.

  9. Check Understanding: • What is the acceleration of a car that goes from 0 to 100 kilometers/hour in 10 seconds? • Suppose a car moving in a straight line steadily increases its speed each second, first from 35-40 km/h, then from 40-45 km/h, then from 45 to 50 km/h. What is its acceleration?

  10. 2.5 Free Fall: How Fast • Do objects accelerate while they fall? Yes! • Free Fall: Freely falling objects only affected by gravity. Air resistance does not affect it. • Instantaneous Speed of Falling Object:(v) = gt g = acceleration of gravity,(9.8m/s2) t = elapsed time

  11. How Fast? Continued… • Objects thrown into air: During upward motion, object slows from initial velocity to zero. It’s speed decreases by 9.8 m/s each second & increases speed at the same rate as it returns to earth. • Note: Velocities are diff. when ball is thrown up & down due to opposite directions. The acceleration or deceleration is always 9.8m/s2.

  12. 2.6 Free Fall: How Far? • Distance of a falling object = ½ gt2 g = (9.8m/s2)

  13. Check Understanding: • If you throw a ball at 40m/s into the air, how long will it take to reach the top? How long will it take for it to reach the bottom again? How fast will it be traveling when it hits the ground? • You and a friend discover a mineshaft and you want to know how deep it goes. You mutually decided to drop a rock down the shaft and it takes the rock 4 seconds to hit the bottom, how deep is the shaft?

  14. 2.7 Graphs of Motion Speed verses Time Graph v = vertical axis t = horizontal axis -Linear relationship between v & t -Line starts at origin since v & t are zero and object starts from rest. -Slope measures speed per time or acceleration (which is constant)

  15. Graphs of Motion Continued… Distance versus Time Graph d = vertical axis t = horizontal axis Parabolic relationship between d & t (2t = 4d) Slope measures speed (speed increase as time passes)

  16. 2.8 Air Resistance & Falling Objects • Air resistance alters the motion of things. (Decreases it’s speed) e.g. piece of paper, feathers • Negligible air resistance = Freely Falling

  17. 2.9 How Fast, How Far, How Quickly How Fast Changes • How Fast (talking about velocity) • v=gt • How Far (talking about distance) • d=½gt2 • How Quickly How Fast Changes (talking about acceleration)

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