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Chapter 13

Chapter 13. Forces. 13-1 Nature of Forces. *Force: push or pull -gives nrg to an object. -Newton said an object in motion stays in motion unless acted upon by an outside force (1 st law of motion) *Friction: force that opposes the motion. -sliding friction.

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Chapter 13

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  1. Chapter 13 Forces

  2. 13-1 Nature of Forces *Force: push or pull -gives nrg to an object

  3. -Newton said an object in motion stays in motion unless acted upon by an outside force (1st law of motion) *Friction: force that opposes the motion

  4. -sliding friction *when two solid surfaces slide over each other -amount depends on two factors 1. Weight 2. Types of surfaces

  5. -rolling friction *object rolls over a surface -oppose motion less than sliding ex: wheels and ball bearings

  6. -fluid friction *object moves through a fluid -all liquids and gases are fluids -usually opposes motion less than sliding friction *Lubricants: change sliding friction to fluid friction

  7. -friction can be helpful ex’s: ????

  8. 13-2 Balanced and Unbalanced Forces *Balanced forces: opp in direction and equal in size -no change in motion -keeps an object moving at constant velocity

  9. *Unbalanced force: not opp and equal -always cause a change in motion

  10. 13-3 Force and Motion • 3 laws of motion explain rest, constant motion, and accelerated motion (Isaac Newton)

  11. -1st Law of Motion *Inertia: tendency of objects to remain in motion or stay at rest -object at rest will remain at rest, and an object in motion will remain in motion, unless acted on by an unbalanced force(ex’s)

  12. -2nd Law of Motion • Force = (mass)(acceleration) N = (kg) (m/s/s) -unbalanced force accel an object in the direction of that force - 1N = 1kg X 1 m/s/s

  13. -3Rd Law of Motion *every action, there is an equal and opposite rxn -all forces come in pairs **Scooter Example**

  14. 13-4 Gravity

  15. -Free fall -All objects accel at the same rate, regardless of their mass *Gravity: attractive force b/all objects in the universe

  16. -Free fall ~near the surface of earth, accel due to gravity 9.8m/s/s -Any falling object meets air resistance *Terminal vel: no longer accel (120mph)

  17. -Projectile Motion *any object thrown in the air ~is always a curve -Once you release a ball the only force acting on it is gravity

  18. Orbital Motion *object that orbits another object ~it is a result of the object’s forward inertia and the downward pull of gravity on the object

  19. -Newton’s Law of Universal Gravitation *all objects in the universe attract each other by the force of gravity -The size of the force depends on: 1)mass 2)distance b/them

  20. 13-5 Weight and Mass -Weight: measure of the force of gravity on an object ~units: newton (N) ~w = m x g -Mass: amount of matter ~mass is constant

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