Question

Suppose your writing desk is tilted a little a book kept on it starts sliding down. What will be the direction of frictional force acting on it?

Answer 1

Direction of frictional force

1. It is said that the desk is tilted a little and the book is sliding down.
2. We know that friction resists motion.
3. So the direction of frictional force is always opposite to the direction of the motion.
4. As it is said that the book is sliding downward, so the direction of the frictional force will be opposite to the direction of the motion of sliding down.

Hence, the direction of the frictional force is opposite to the direction of the motion of the book.