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Types of Forces

Types of Forces. Four Main Forces in Universe. Gravity F g . Electromagnetic EM Strong Nuclear Strong or Nuclear Weak Nuclear Weak. All Forces fall into one of the above categories. Common Forces. Weight depends on gravity, Mass does not. Weight F g = mg gravity interaction with mass.

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Types of Forces

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  1. Types of Forces

  2. Four Main Forces in Universe • Gravity Fg. • Electromagnetic EM • Strong Nuclear Strong or Nuclear • Weak Nuclear Weak • All Forces fall into one of the above categories.

  3. Common Forces Weight depends on gravity, Mass does not. WeightFg = mg gravity interaction with mass. What is mass? Amount of matter in object.

  4. Normal Force (reaction force) – • perpendicular to the surfaces in contact. • Opposite to weight on horizontal surface. • Fn = -W

  5. What if you’re leaning on a wall. Where is the normal force?

  6. Where is it now?

  7. Which way is friction? Sliding Friction – forceacts at contact between surfaces. Direction of friction opposes velocity or attempted velocity. Ff = mFn m is constant

  8. Which way is the book moving? Right Left The box is not moving.

  9. Tension – • transmitted through string, rope, or wire by forces at each end.

  10. Air Resistance – air friction. Big reason for bad fuel economy in cars.

  11. Spring or Elastic Force – Force applied by stretched or compressed spring described byHooke’s Law.

  12. Magnetic Force

  13. Electrical

  14. Force is a vector quantity. It has direction.Acceleration – Dv – is always in the same direction as the net force!!

  15. Free Body Diagrams • Diagrams to show relative magnitude & direction of all vector forces acting on a body. • Sizes of arrows show magnitude of force. • Arrowhead shows direction of forces.

  16. What can you say for sure about the object in the free body diagram below? • 1. It is at rest. • 2. It is in motion to the left. • 3. It is in motion to the right • 4. Notenough information to know.

  17. Balanced & Unbalanced Forces

  18. An unbalanced force is a resultant or net force. What is the Fnet? What can you say about the motion? 4 N 12 N Fnet = - 8 N or 8 N left The object shows Acceleration left.

  19. A bird flies with a constant velocity to the left at a constant altitude. What is the free body diagram?

  20. V = 0 up so no Fnet up. F bird cancels Fgrav. Const v horiz. So no Fnet left. Friction balanced by force of bird left. F bird up F bird left F air fric F grav

  21. Assignment • Handout “Free Body Diagrams”

  22. Number One

  23. Number Two

  24. Number Three

  25. Number Four

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