Physics Concept Question?

#1 is not true because the frictional force is equal to the

gravitational force or the books would be moving.

#3 is incorrect also because there is friction applied to both sides of both books.

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These statements are correct:

2. If you doubled the horizontal force you applied to the textbook, the friction forces would stay the same.

4. The vertical forces on the books are gravity and friction.

Yes. 2 and 4.

we have gravity and friction.

we also have other forces at work on the book and the manual

they are so weak in relation to our first two forces that we might

not even consider them

they are;

buoyancy in relation to earths atmosphere , the air pressure causes them to lift up a little bit. this might be worth considering though because if you were underwater the books might have a greater chance of floating up instead of falling down(this could also happen if your books were made out of *wink* that hydrogen gas paper that the government has but wont tell anybody about.

angular acceleration because the books are on a spinning planet, this would have a more dramatic effect if you and the books were standing on a very small spinning planet with little gravity.

beyond that though there are a great many forces that just effect the main forces we are considering so i wont bore anybody with details of such :)

4. The vertical forces on the books are gravity and friction.

option 4 is correct.

The gravitational force which would have made the books fall is balanced by the frictional force between the wall and lab manual and also that between the books.

4 is right

1 and 2 - not enought data

3 - bull

4 - right (assuming the wall is vertical)