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L5

  1. 1. Chapter 4 Newton’s First Law of Motion M.Atanasiu. Text - Conceptual Physics (Hewitt) Based on Dr. Bruton’s lectures at Austin State University
  2. 2. Sir Isaac Newton (1643 – 1727) > Born shortly after Galileo died > Inventor of Calculus > Known for his laws of motion
  3. 3. Isaac Newton's own first edition copy of his Philosophiae Naturalis Principia Mathematica with his handwritten corrections for the second edition.
  4. 7. A reputed descendant of Newton's apple tree, found in the Botanic Gardens in Cambridge.
  5. 9. “ If I have seen further it is by standing on the shoulders of giants”
  6. 10. Who are these giants?
  7. 11. Aristotle on Motion (350 BC) <ul><li>Aristotle attempted to understand motion by classifying motion as either </li></ul><ul><ul><ul><li>(a) natural motion </li></ul></ul></ul><ul><ul><ul><ul><ul><li>forces acting at a distance </li></ul></ul></ul></ul></ul><ul><ul><ul><li>(b) or violent motion </li></ul></ul></ul><ul><ul><ul><ul><ul><li>contact forces </li></ul></ul></ul></ul></ul>
  8. 12. <ul><li>“ Large objects tend to 'strive harder'.” </li></ul><ul><li>He stated that “The Earth remains at rest.” </li></ul>
  9. 13. <ul><li>Geocentric Model - Earth Centered Universe </li></ul>
  10. 15. Copernicus (1500's) <ul><li>&quot;The Earth and planets orbit the Sun.” </li></ul><ul><li>He reasoned this from his astronomical observations. </li></ul>
  11. 16. Galileo (1600's) <ul><li>Scientist who supported Copernicus </li></ul><ul><li>Dropped objects with different weights from the Leaning Tower of Pisa </li></ul><ul><li>Found that all objects fall at the same rate if you can account for air resistance </li></ul><ul><li>http://www.youtube.com/watch?v=YD6JYdKxRjo Pisa </li></ul><ul><li>http://www.youtube.com/watch?v=x7dUgiKzLSc Pisa </li></ul><ul><li>http://www.youtube.com/watch?v=WOvwwO-l4ps Moon </li></ul>
  12. 17. <ul><li>Friction - a force that resists motion </li></ul><ul><ul><ul><li>e.g. air resistance and sliding on rough surfaces </li></ul></ul></ul><ul><li>Inertia - the resistance of an object to change in its state of motion </li></ul><ul><ul><li>“ Sluggishness” </li></ul></ul><ul><li>http://www.youtube.com/watch?v=w3Vhz9b6iKg Bow and Arrow </li></ul><ul><li>Demo: Ball and incline plane </li></ul>
  13. 18. Galileo’s Incline Planes
  14. 19. Isaac Newton (1642-1727) <ul><li>His three laws of motion first appeared in his book called Principia . </li></ul>
  15. 20. Newton’s First Law <ul><li>a.k.a “Law of Inertia” </li></ul><ul><li>A body remains at rest or moves in a straight line at a constant speed unless acted upon by a force . </li></ul>
  16. 21. Newton’s First Law Examples <ul><li>Weight and string </li></ul><ul><li>Card, cup, and coin </li></ul><ul><li>Fixing a Hammer </li></ul><ul><li>Demo - Table setting </li></ul><ul><ul><li>http://www. youtube .com/watch?v=T9KPwNeCdSg </li></ul></ul>
  17. 22. Mass <ul><li>the quantity of matter in an object </li></ul><ul><li>the measurement of the inertia </li></ul><ul><li>measured in kilograms (kg) </li></ul>
  18. 23. Weight <ul><li>the force upon an object due to gravity </li></ul><ul><li>Weight = Mass  Acceleration of gravity </li></ul><ul><li>W = mg </li></ul><ul><li>measured in Newtons (N) in the metric system or pounds (lb) in the British system </li></ul>
  19. 24. <ul><li>The weight of a 10 kg brick is... </li></ul><ul><ul><ul><li>A) 98 N </li></ul></ul></ul><ul><ul><ul><li>B) 10 kg </li></ul></ul></ul><ul><ul><ul><li>C) 9.8 kg </li></ul></ul></ul><ul><ul><ul><li>D) 10 N </li></ul></ul></ul><ul><ul><ul><li>E) 98 kg </li></ul></ul></ul>
  20. 25. Mass and Weight should not be confused with... <ul><li>Volume </li></ul><ul><ul><ul><li>the quantity of space an object occupies </li></ul></ul></ul><ul><li>Density </li></ul><ul><ul><ul><li>the quantity mass per unit volume </li></ul></ul></ul>
  21. 26. Mass and Weight <ul><li>On the Moon the gravitational force is only 1/6 as strong as on the Earth. </li></ul><ul><li>In space you are “weightless” but not “massless”. </li></ul><ul><li>Your mass does not depend on where your are. </li></ul><ul><ul><ul><li>(e.g. Earth, Moon, or space). </li></ul></ul></ul>
  22. 27. Weight Location Mass Earth Moon Space 18.4 kg 18.4 kg 18.4 kg 180 N 30 N 0 N
  23. 28. <ul><li>A force or a combination of forces produces changes in motion (accelerations). </li></ul>10 N NET FORCE 10 N 10 N = 20 N 10 N 10 N = 0 N 10 N 20 N = m m m m m m
  24. 29. THE EQUILIBRIUM RULE Examples of Mechanical Equilibrium: Hanging from a tree Weighing yourself on a set of scales Computer setting on a table Car parked on an incline Normal up Weight down Weight down Weight down Weight down Scales pushing up Tree pulling up Normal Friction
  25. 30. The Equilibrium Rule <ul><li>The vector sum of all forces on a body in equilibrium is zero </li></ul>
  26. 31. <ul><li>A table can supply an upward support force also known as a normal force . </li></ul><ul><li>When we say “normal to” we are saying “at right angles to”. </li></ul>SUPPORT FORCE Scales pushing up Weight down Normal up Weight down
  27. 32. <ul><li>Equilibrium is a state of no change. </li></ul><ul><li>If an object moves in a straight line with no change in speed, it is in equilibrium. </li></ul>EQUILIBRIUM OF MOVING THINGS Examples: Driving at constant velocity Force from road Air Resistance Normal up Weight down Terminal velocity in parachuting Weight down Air resistance
  28. 33. <ul><li>It is hard to detect the motion of the earth because we are moving with it. </li></ul><ul><li>Early science could not predict large enough forces to move the earth. </li></ul><ul><li>Can Hewitt’s bird drop down and catch the worm if the Earth moves at 30 km/s? </li></ul>THE MOVING EARTH
  29. 34. Chapter 4 Review Questions
  30. 35. Which person below is most highly recognized for proposing a heliocentric universe? <ul><li>(a) Aristotle </li></ul><ul><li>(b) Newton </li></ul><ul><li>(c) Galileo </li></ul><ul><li>(d) Copernicus </li></ul>
  31. 36. If an object weighs 10 N, what must the air resistance force be if the object is falling and has reached terminal velocity? (a) 10 N (b) 32 N (c) there is no way of telling without knowing what the value of the terminal velocity is
  32. 37. Newton's concept of motion said that the natural state of an object was <ul><li>(a) constant velocity </li></ul><ul><li>(b) constant acceleration </li></ul><ul><li>(c) constant net force </li></ul>
  33. 38. Classwork Questions <ul><li>P.57 / 22, 24 </li></ul><ul><li>(use g = 9.81 m/s 2 ) </li></ul>
  34. 39. p.57 / 22 <ul><li>Calculate in newtons the weight of a 2000-kg elephant. </li></ul>
  35. 40. p.57 / 24 <ul><li>An apple weighs about 1N. What is its mass in kilograms? </li></ul>
  36. 41. Homework Questions <ul><li>p.57 / 21, 23, 25 </li></ul><ul><li>(use g = 9.81 m/s 2 ) </li></ul>
  37. 42. p.57 /21 <ul><li>If a woman has a mass of 50kg, calculate her weight in newtons. </li></ul>
  38. 43. p.57 / 23 <ul><li>Calculate in newtons the weight of a 2.5kg melon. </li></ul>
  39. 44. p.57 / 25 <ul><li>Susie Small finds she weighs 300N. Calculate her mass. </li></ul>
  40. 45. End L5 www.slideshare.net/DMS_physics

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