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Objectives:
       -Students will be able to define friction and apply it to everyday life

       -Students will be able to solve for all types of friction
 

Friction:A force which opposes motion of any other force, it always creates heat or sound.  Friction takes away from kinetic energy. It can cause deceleration, to cause things to slow down or come to a stop.

    Sliding Frictional Force: When the surface of one object slides over another each object creates a frictional force on the other

  Static Frictional Force: Acts even when there is no relative motion between the surface of two objects, this makes it difficult to slide a heavy box across and rough floor.  Once two forces begin sliding static friction is no longer a concern

Real Life Applications:
    - Brakes
    - Engines
    - Anything sliding over a surface
    - Air Friction
    - Matches
    - It is in everything we do

Formula:

               FF = FN x u                  FF - Force Friction
                                            FN- Force Normal
                                            u -Coefficient of friction

       *You can solve for force normal by taking the force weight of the object and multiplying it by the cosine of the angle.  Force weight is just the weight of the object multiplied by gravity (9.8 m/s²).

    *All forces are measured in Newtons (N)
0
Coefficient of Friction: The coefficient of friction ranges from 0-1.  Zero meaning there is no friction, something like oil on ice, and 1 having the most friction, something like sandpaper. It is a unitless number.

Example Problems:

1.   FW= 125N
                  FN= 102.4N
                  The angle= 35 degrees
                u= .5
Solve for Ff
 
 

Answer:
    Ff=  102.4N x .5
        = 51.2N

2. FW= 29.5N
                  The angle= 12 degrees
                 u= .12

Solve for Ff
 

Answer:
    First solve for FN
    FN=29.5N x cos(35)
        =24.16N
    Then solve for FF
       FF= 24.16N x .12
        = 2.9N

3. M= 5Kg
               The angle= 37 degrees
               u= .43

Solve for FF
 

Answer:
   First you need to solve for FW since they only have given you the mass
FW= mg
    =5Kg x 9.8m/s²
    =49N

  Then with the FW solve for FN
FN= FW x cos(37)
    = 49N x cos(37)
    = 39.13N

Finally solve for FF
FF= FN x u
   = 39.13N x .43
    =16.83N
 
 

Links:
 PhysLink.com
 Friction Explained