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Newton’s Laws

Newton’s Laws. General Physics Summer 2013. Isaac Newton.

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Newton’s Laws

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  1. Newton’s Laws • General Physics Summer 2013

  2. Isaac Newton • “This most beautiful system of the sun, planets, and comets, could only proceed from the counsel and dominion of an intelligent and powerful Being....This Being governs all things, not as the soul of the world, but as Lord over all; and on account of his dominion he is wont to be called Lord God ‘pantokrator,’ or Universal Ruler...”

  3. Real Physics! • Mass vs. Force • Newton’s 3 laws: • An object at rest stays at rest or an object in motion stays in motion, unless acted upon by an outside force. (constant in magnitude and direction) • For every action there is an equal and opposite reaction

  4. Application • How to always win at tug of war

  5. Why do we have friction?

  6. How do we describe Friction? • Static Vs. Kinetic • Static: • Kinetic: • Friction always opposes motion

  7. Normal Force -- details • Normal means perpendicular to the surface • The Normal force automatically adjusts until the surface breaks

  8. Example • A buggy is pulled down the road by a horse who exerts a constant force of 65 N. The buggy has a mass of 150 Kg. • Why doesn’t the buggy get faster and faster and faster? • What is the weight of the buggy? • What are the forces on the horse?

  9. Elevator • Sally-Sue has a mass of 45 Kg, she stands on a scale in the elevator. What does the scale tell her her weight is in the following situations? The elevator has a starting and stopping acceleration of 3 m/s2. • Before it starts. After it starts. As it is stopping at the top floor. As it is starting again from the top floor. As it is stopping at the bottom floor.

  10. Example • Jim-Bob pulls a 50 Kg sled along the flat ground. The rope has an angle of 40o to the ground. If coefficients of static and kinetic friction are 0.4 and 0.3: • How much force does it take to start the sled moving? • Once it starts sliding, what is the minimum force required to maintain a constant velocity

  11. Inclined Planes • If the mass is 2.00 Kg, and the angle of inclination is 30o, what is the minimum force required to hold the block in place? What is the normal force? How would the problem change if there were friction?

  12. Tension Problem • Problem 4.17 • Find the tension in all three cables.

  13. Pulleys • Problem 4.60 • If the coefficient of static and kinetic friction is 0.49 and 0.32 respectively, • Will the system move? • If so, how fast, and which way? • What is the tension in the string?

  14. Acknowledgements • tug o’ war picture: http://www.redbubble.com/people/andyjones/art/4981318-2-digging-in-irish-national-tug-of-war-championship-new-ross-county-wexford-ireland • buggy picture: http://www.megdanielsphoto.com/galleries/environmental_and_landscapes/pages/horse%20and%20buggy.htm • Sanding picture: http://www.hotrod.com/howto/drp_0606_paint_stripping_basics_tips/photo_04.html • Normal surfaces: http://www.britannica.com/EBchecked/media/67388/The-normal-or-perpendicular-at-each-point-of-a-surface • Double inclined plane: Tipler and Mosca • All other pictures: Cengage learning (our textbook)

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