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4 4 notes

  1. 1. 4-4 Review
  2. 2. Normal Force• Equal in magnitude to Fg, but opposite in direction• Perpendicular to the surface• Fn = mg(cos of angle) –Angle is between normal force and a vertical line, and also contact surface horizontal line –See Figure 4-20 (b)
  3. 3. Static Friction• Static friction (Fs) – resistance force that keeps an object from moving – Small push on a heavy object doesn’t cause it to move – Equal to the applied force as long as the object doesn’t move (Fs = -Fapplied) – Fs,max – applied force is a great as it can be without causing the object to move
  4. 4. Friction (cont.)• Kinetic friction (Fk) – force that opposes an object’s motion – Always less than Fs,max – Net external force acting on an object is equal to difference between applied force and force of kinetic friction (F - Fk) – Depends on surfaces in contact
  5. 5. Friction (cont.)• Coefficient of friction – expresses the dependence of frictional forces on particular surfaces in contact• Represented by lower case greek letter,• See formulas and table 4.2 on page 144

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