The origin of friction…

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Presentation transcript:

The origin of friction… This roughness is unpredictable and definitely nonlinear!

v f There are two kinds of friction Kinetic when the surfaces are slipping past each other v f Kinetic friction always opposes the relative motion

v f v = 0 f Fext There are two kinds of friction Kinetic when the surfaces are slipping past each other v f Kinetic friction always opposes the relative motion v = 0 Static when the surfaces are not slipping f Fext Static friction opposes the force that is trying to slide the objects

This is our model of kinetic friction Kinetic friction is proportional to the normal force between the two objects: This is our model of kinetic friction

When you slide a 50.0 g salt shaker to your friend at the other side of the table, you give it an initial speed of 1.15 m/s. The salt shaker comes to rest in 0.840 m. Assume constant acceleration. What is the coefficient of kinetic friction between the shaker and the table?

When you slide a 50.0 g salt shaker to your friend at the other side of the table, you give it an initial speed of 1.15 m/s. The salt shaker comes to rest in 0.840 m. Assume constant acceleration. What is the coefficient of kinetic friction between the shaker and the table? For how much time does the salt shaker slide before coming to rest?

A copper block, starting from rest, slides down an inclined steel ramp that is 75 cm long. The ramp is inclined 42º to the horizontal. What is the block’s speed when it reaches the bottom of the ramp?

Static Friction

Static Friction

As you drive down a dry road (doing the speed limit, of course) is the friction between your tires and the road static friction or kinetic friction? Static Kinetic There’s no way to tell

Tension in a rope or string Molecular forces in a string that is stretched pull back towards the middle The molecules resist being torn apart Ropes always PULL (They transmit force from one object to another)

The tension in a rope is the same everywhere in a rope

NOTE: Ideal pulley Ideal rope