# Question about Friction force

The harder I push a book to a wall, the larger is the friction force, since friction is (coefficient of friction (times) the force I use).

Why won't the friction force make the object go up instead of stay where it is since the friction worse can get arbitrarily large while gravitational force is constant?

(not a homework question but one I thought of)(English is my 2nd language)

## Answers and Replies

jack action
Science Advisor
Gold Member
Friction is a reactive force, so you need another force to create the friction. In your case, the force is the weight of the book so the friction force will never be greater than the weight of the book.

What the coefficient of friction times the normal force equation tells you is the MAXIMUM force that friction can handle. So by pushing harder you do not increase friction, but if you would add another force pushing the book down (say adding weight on it), the friction force could still resists the increased downward force.

It is not clear in your original statement which direction you are pushing the book (parallel to the wall or perpendicular to the wall?).

What Jack said was very good.

(parallel to the wall or perpendicular to the wall?)

Perpendicular.