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Chapter 2

Chapter 2. Motion. 2 .1 Distance and Displacement. Motion : The change in position of an object as compared with a reference point Reference point : System of objects that are not moving (stationary) in respect to one another. Distance. Length of path between 2 points

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Chapter 2

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  1. Chapter 2 Motion

  2. 2.1 Distance and Displacement • Motion: The change in position of an object as compared with a reference point • Reference point: System of objects that are not moving (stationary) in respect to one another

  3. Distance • Length of path between 2 points • May not be straight line (shortest path) • Units: meters (m), km, miles, cm, etc. • Ex: Roads/streets we drive

  4. Displacement • The direction and length in a straight line from start to end • ALWAYS includes direction from start point • Ex: walk 5 blocks north from McDonald’s • Ex: roller coaster ride displacement = 0

  5. Speed • How fast in a given amount of time • Distance traveled by object • Time to travel that distance • Units: • m/s • mi/hr or mph • km/hr

  6. Speed Types • Average Speed- Calculated speed for trip • Ex) Ran marathon at 6 mi/hr • Instantaneous Speed- speed at exact moment • Ex) speedometer reading = 55 mi/hr • Object going an equal distance in equal amounts of time = Constant speed (not speeding up or slowing down)

  7. Speeds • Doesn't tell the direction • 45 mph • 4 m/s

  8. Calculating Speed & Avg. Speed • Expressed in m/s • Speed = Distance/Time • Or S = d/t • Ex: A car traveling at a constant speed and it goes and distance of 645 m in 25 s. What is the car’s speed? • S = d/t • S = 645m/25s • S = 25.8 m/s

  9. Distance - Time Graphs • Graphs show speed/velocity • Time (independent variable) -> x-axis • Distance (dependent variable) -> y-axis

  10. Distance - Time Graph

  11. Distance -Time Graphs • Slope of line = speed or velocity • Straight line = constant speed (cruise control) • Steeper slope = faster speed

  12. Distance - Time Graphs • Horizontal (flat) line = object not moving • Exs: stopped at red light, parked, at store

  13. Distance - Time Graphs • Negative slope = went backwards (neg. displacement) • Ex: went to store, shopped, and back home

  14. Velocity • Measurements: • Speed: m/s, km/h, or m/h • Direction: • N (NE, NW), S (SE, SW), East, and West • Describes both speed and direction of motion • Must give how “fast” and direction the object is going • Ex: 45 km going South

  15. 2.2 Acceleration • Can be described as changes in speed, direction, or changes in both • Small value = increasing gradually • Larger value = speeding up more rapidly • The slope of a speed-time graph is acceleration

  16. Acceleration (pg. 49 -50) • Positive Acceleration – velocity increases or speeds up (gives a positive slope ) • Negative Acceleration – velocity decreases or slows down (gives a negative slope ) • Horizontal line – on a velocity-time graph; stays constant, velocity does not change (-----)

  17. Changes in Acceleration • Any change in how fast or change in direction • Speed up • Slow down • Turn a corner • Go around a curve

  18. Calculating Acceleration • Acceleration = change in velocity/time • a = (final velocity – initial velocity)/time • Measured in meters/second/second • a = vf - vi/t

  19. Calculating Acceleration • Calculating positive acceleration = pos. # (speeding up) • Ex: a = (80m/s – 0m/s)/20s = 4m/s • Calculating negative acceleration = neg. # (slowing down) • Ex: a = (0m/s – 3m/s)/2s = 1.5 m/s

  20. Force • Causes velocity change • Unit = Newton (N) • Net Force - combo of all forces acting on object • Net force = 0 • Either stopped or constant speed

  21. Force • 2 Types of forces: • Balanced Forces - net force = 0 • Forces cancel out • Ex) Fair tug of war • Unbalanced Forces - net force not = 0 • One force is stronger • Car vs Train

  22. Balanced Forces

  23. Unbalanced Forces

  24. Isaac Newton • Physicist who described relationship between force & motion • 3 Laws: Newton’s Laws of Motion

  25. Newton’s 1st Law • AKA – Law of Inertia • “An object at rest stays at rest, and an object in motion stays in motion, unless acted upon by an unbalanced force.” • Inertia = tendency of object to stay at rest • Exs: car crashes, magician table cloth trick

  26. 1st Law

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