FRICTION NOTES

WHAT IS FRICTION?

What are the types of friction?

What causes it?

Always depends on __________________

Which type of friction is strongest?

How do we measure friction?

What is the coefficicnt of friction?

Ff= m FN

What is the normal force?

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A skier slides down a slope. What force causes him to go down?

What force opposes him?

What changes in environmental conditions might cause a change in the frictional force?

FRICTION PROBLEMS

1) D = (Vi+Vf) * T                             3) Vf = Vi + A*T

2

2) Vavg = (Vi+Vf)                             4) D = Vi*T + ½*A*T2

2

5) Vf2 = Vi2 + 2*A*D

Newton’s Laws

Fnet = m * A                           F1 = F2

Weight = m * g                       Ff= m FN= m W = m mg ). m= Ff/ FN

1) What net external force is required to give a 25 kg suitcase an acceleration of 2.2 m/s2 to the right? Draw a free body diagram. If it is wood on wood (m  = .2 what is the force of the push?

2) What acceleration will you give to a 24.3 kg box if you push it with a force of 85.5 N? If it is aluminum on steel so (m  = .47  what is the acceleration?)

3) A 1850 kg car is moving to the right at a constant velocity of 1.44 m/s. What is the net force on the cart? If it is rubber on concrete so (m  = .8  what is the force?)

4) A man is pushing a 200 Newton box with a force of 50 Newtons along the floor. A dog is pushing against him with a force of 4 N . What is the acceleration of the box? Draw a free body diagram for the box. If it is glass on glass so (m  = .4  what is the acceleration?)

9) A 1200 kg boat moves through the water with two forces acting on it. One is a 2100 N forward push by the motor, and the other is a 1800 N resistive friction force of the water.

What is the coefficient of friction?

** Honors:

13) A block with a mass of 50 kg is sliding down a  ramp, that is wood on wood,  that is at an angle of  60 degrees. What is the component of the force causing it to slide? What is the force of of friction? What is its acceleration? Draw a picture and force diagram.