Force of friciton always act opposite to direction of motion of object So it is negative force

Example

When a ball is thrown with a force, it is postive work (as ball moves in direction of force applied)

However, ball stops after some time (it is negative work as ball moves opposite to direction of force applied)

It is because of the negative work(force is in the direction opposite to motion) done by the friction on the ball.

  1. Class 9
  2. Chapter 11 Class 9 - Work and Energy (Term 2)

About the Author

CA Maninder Singh's photo - Founder at Teachoo
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo