Physics is a drag!

 The force that resist motion  Represented by symbol F f  Measured in Newtons  Acts parallel to the surface in contact  Acts opposite to the direction of motion

 Depends on the nature of the materials in contact.  Independent of speed or area of contact.  Proportional to the force pressing the surfaces together (same as F N )  2 kinds  Static (stationary-force you must overcome to start moving)  Kinetic (between surfaces that are moving)

 Symbol : µ  A value that represent the amount of friction between 2 surfaces (no units)  Calculated by taking F f /F N  µ s : coefficient of static friction  µ k : coefficient of kinetic friction  To find Ff simply multiply µ by F N

Fg FNFN FaFa FfFf F f = µF N F N = Fg but why? But how do you find Fg? Fg = mg =m(9.80m/s 2 )

 Friction is caused by 2 surfaces rubbing together.  Drag or air resistance is the common term used for object rubbing against air (air resistance). It mainly depends on 2 things  The speed of the object.  The surface area of the object  Traction is the common term used for objects rubbing against a solid surface. This mainly depends on 2 different things  The force pressing the surfaces together which has to do with the weight of the object.  The texture of the surfaces in contact. *** We will concentrate on calculating friction between solids or traction in this course. As a general rule we will ignore drag for object not in free fall because the air resistance is very small compared to the traction.