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  • 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. Sir Isaac Newton (1643 – 1727) > Born shortly after Galileo died > Inventor of Calculus > Known for his laws of motion
  • 3. Isaac Newton's own first edition copy of his Philosophiae Naturalis Principia Mathematica with his handwritten corrections for the second edition.
  • 4.  
  • 5.  
  • 6.  
  • 7. A reputed descendant of Newton's apple tree, found in the Botanic Gardens in Cambridge.
  • 8.  
  • 9. “ If I have seen further it is by standing on the shoulders of giants”
  • 10. Who are these giants?
  • 11. Aristotle on Motion (350 BC)
    • Aristotle attempted to understand motion by classifying motion as either
        • (a) natural motion
            • forces acting at a distance
        • (b) or violent motion
            • contact forces
  • 12.
    • “ Large objects tend to 'strive harder'.”
    • He stated that “The Earth remains at rest.”
  • 13.
    • Geocentric Model - Earth Centered Universe
  • 14.  
  • 15. Copernicus (1500's)
    • "The Earth and planets orbit the Sun.”
    • He reasoned this from his astronomical observations.
  • 16. Galileo (1600's)
    • Scientist who supported Copernicus
    • Dropped objects with different weights from the Leaning Tower of Pisa
    • Found that all objects fall at the same rate if you can account for air resistance
    • http://www.youtube.com/watch?v=YD6JYdKxRjo Pisa
    • http://www.youtube.com/watch?v=x7dUgiKzLSc Pisa
    • http://www.youtube.com/watch?v=WOvwwO-l4ps Moon
  • 17.
    • Friction - a force that resists motion
        • e.g. air resistance and sliding on rough surfaces
    • Inertia - the resistance of an object to change in its state of motion
      • “ Sluggishness”
    • http://www.youtube.com/watch?v=w3Vhz9b6iKg Bow and Arrow
    • Demo: Ball and incline plane
  • 18. Galileo’s Incline Planes
  • 19. Isaac Newton (1642-1727)
    • His three laws of motion first appeared in his book called Principia .
  • 20. Newton’s First Law
    • a.k.a “Law of Inertia”
    • A body remains at rest or moves in a straight line at a constant speed unless acted upon by a force .
  • 21. Newton’s First Law Examples
    • Weight and string
    • Card, cup, and coin
    • Fixing a Hammer
    • Demo - Table setting
      • http://www. youtube .com/watch?v=T9KPwNeCdSg
  • 22. Mass
    • the quantity of matter in an object
    • the measurement of the inertia
    • measured in kilograms (kg)
  • 23. Weight
    • the force upon an object due to gravity
    • Weight = Mass  Acceleration of gravity
    • W = mg
    • measured in Newtons (N) in the metric system or pounds (lb) in the British system
  • 24.
    • The weight of a 10 kg brick is...
        • A) 98 N
        • B) 10 kg
        • C) 9.8 kg
        • D) 10 N
        • E) 98 kg
  • 25. Mass and Weight should not be confused with...
    • Volume
        • the quantity of space an object occupies
    • Density
        • the quantity mass per unit volume
  • 26. Mass and Weight
    • On the Moon the gravitational force is only 1/6 as strong as on the Earth.
    • In space you are “weightless” but not “massless”.
    • Your mass does not depend on where your are.
        • (e.g. Earth, Moon, or space).
  • 27. Weight Location Mass Earth Moon Space 18.4 kg 18.4 kg 18.4 kg 180 N 30 N 0 N
  • 28.
    • A force or a combination of forces produces changes in motion (accelerations).
    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
  • 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
  • 30. The Equilibrium Rule
    • The vector sum of all forces on a body in equilibrium is zero
  • 31.
    • A table can supply an upward support force also known as a normal force .
    • When we say “normal to” we are saying “at right angles to”.
    SUPPORT FORCE Scales pushing up Weight down Normal up Weight down
  • 32.
    • Equilibrium is a state of no change.
    • If an object moves in a straight line with no change in speed, it is in equilibrium.
    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
  • 33.
    • It is hard to detect the motion of the earth because we are moving with it.
    • Early science could not predict large enough forces to move the earth.
    • Can Hewitt’s bird drop down and catch the worm if the Earth moves at 30 km/s?
    THE MOVING EARTH
  • 34. Chapter 4 Review Questions
  • 35. Which person below is most highly recognized for proposing a heliocentric universe?
    • (a) Aristotle
    • (b) Newton
    • (c) Galileo
    • (d) Copernicus
  • 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
  • 37. Newton's concept of motion said that the natural state of an object was
    • (a) constant velocity
    • (b) constant acceleration
    • (c) constant net force
  • 38. Classwork Questions
    • P.57 / 22, 24
    • (use g = 9.81 m/s 2 )
  • 39. p.57 / 22
    • Calculate in newtons the weight of a 2000-kg elephant.
  • 40. p.57 / 24
    • An apple weighs about 1N. What is its mass in kilograms?
  • 41. Homework Questions
    • p.57 / 21, 23, 25
    • (use g = 9.81 m/s 2 )
  • 42. p.57 /21
    • If a woman has a mass of 50kg, calculate her weight in newtons.
  • 43. p.57 / 23
    • Calculate in newtons the weight of a 2.5kg melon.
  • 44. p.57 / 25
    • Susie Small finds she weighs 300N. Calculate her mass.
  • 45. End L5 www.slideshare.net/DMS_physics