## adeniyta 3 years ago Hey- could someone please help me with the free body diagrams. If there is a hand pushing on a book,laying on a table- what are the forces acting on the book? I thought they were normal force, force of hand and gravity.

1. eashmore

Consider the presence of a friction force as well. It will be directed opposite the force of the hand. Otherwise, the three you named is it.

Will there be friction, if the hand is acting upon the book from above?

3. UnkleRhaukus

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Okay thank you this was very helpful.

If the book is being pushed up a wall what forces would affect the book? Here is what I think?

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7. eashmore

Gravity does not act on the book in the horizontal direction. If the applied force is vertical, there will be no normal force between the book and the wall and thereby no friction force. |dw:1334635152412:dw|

Isn't there friction because there are two surfaces in contact with each other?

9. quarkine

yeah but only is when surfaces are moving wrt each other..

10. eashmore

From Coulomb's Friction model, there must be a normal force present between the two. In this basic case, there is no normal force between the wall and the book and therefore, no friction force.

11. eashmore

Coulomb's friction model is\[F_f = mu N\]

12. eashmore

We can't simply create a normal force because we desire to have friction.

Hmm.... this is interesting that's seems kind of strange, but I understand it.

I have one more quick question (thank you for your patience): If there are for links connected together and are suspended by a rope. Here is what I thinks and a picture:

|dw:1334636071637:dw|

The force on 1= tension of rope and weight of rings 2,3 and 4. The force on 2= tension caused by chain link 2 and force of weight of 3 and 4. The force on 3 = tension caused by chain links 1 and 2 and weight of 4. The force on 4= tension caused by chain links 1,2 and 3 and force of gravity.

17. eashmore

Indeed. Realize that tension of the rope must equal the weight of all four ring if the links aren't moving.

k- good I think I get the concept. Thank you a ton- you are very patient.

19. eashmore

You're very welcome!