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Forces and Newton’s Laws of Motion

Forces and Newton’s Laws of Motion. Sections 4.1 – 4.3. 4.1 The Concepts of Force and Mass. Force  Push or Pull Contact Forces  pulling on rope, pushing on ball Non-contact Forces  gravity pulling object Mass  How much matter Sir Isaac Newton studied force and mass

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Forces and Newton’s Laws of Motion

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  1. Forces and Newton’s Laws of Motion Sections 4.1 – 4.3

  2. 4.1 The Concepts of Force and Mass • Force  Push or Pull • Contact Forces  pulling on rope, pushing on ball • Non-contact Forces  gravity pulling object • Mass  How much matter • Sir Isaac Newton studied force and mass • Made Newton’s Laws of Motion

  3. 4.2 Newton’s First Law of Motion • Ice Hockey • When nothing happening puck sits on ice • After hit, puck moves in straight line until hits something

  4. Newton’s First Law of Motion • An object continues in a state of rest or in a state of motion at a constant speed along a straight line, unless compelled to change that state by a net force.

  5. Net Force • Net Force  Vector sum of all forces • Net Force required to change velocity

  6. Inertia and Mass • Takes more force to change velocity of some objects • Inertia  tendency to stay at rest or in constant motion • Mass  measurement of inertia • Kilogram (kg)

  7. Physics of Seat Belts

  8. An Inertial Reference Frame • Reference frame in which Newton’s law of inertia is valid. • Noninertial frame  reference frames that are accelerating.

  9. 4.3 Newton’s Second Law of Motion • What happens when a net force is applied to a hockey puck? • Accelerates (changes velocity) • More net force  More acceleration

  10. Newton’s Second Law Components • Force • Mass

  11. Newton’s Second Law of Motion • When a net external force F acts on an object of mass, m, the acceleration, a, that results is directly proportional to the net force and has a magnitude that is inversely proportional to the mass. The direction of the acceleration is the same as the direction of the net force. OR

  12. Newton’s Second Law of Motion F = ma

  13. Force • External force • Come from the environment • Internal force • One part of object pushing (or pulling) another part of object

  14. Unit of Force • Newton (N) • Force = mass x acceleration • N = kg x m/s2 • N = kg m/s2

  15. Calculations with Newton’s 2nd Law • F needed • Free-body diagram • Draw only forces acting on the object • Represent the forces are vector arrows

  16. A = -200 N C = +304 N B = -278 N D = +189 N Example • Four people are having a tug-o-war game. Ashley pulls left with 200 N, Bert pulls left with 278 N, Charlie pulls right with 304 N, and Dannie pulls right with 189 N. What is the net force, acceleration of the 5 kg rope, and who wins the game? • Free-body diagram

  17. A = -200 N C = +304 N B = -278 N D = +189 N Example • What is the net force, acceleration of the 5 kg rope, and who wins the game? • F = +15N • a= 3 m/s2 • Charlie and Dannie win!

  18. Practice Work • You should be able to try • 115 #CQ 1- 5, P 1- 7 • Total of 13 problems

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