# Sign of the work done by dissipation forces

I don't understand this passage from the book I'm reading:

Physically, it is clear that a system cannot be conservative if friction or other dissipation forces are present, because $$\mathbf{F}\cdot d\mathbf{s}$$ due to friction is always positive and the integral cannot vanish.

Why Is the work done by friction always positive? If $$\mathbf{F}$$ is opposite to the force moving the body, the sign should vary depending on the sign of $$d\mathbf{s}$$

• The work done by friction relative to the surface the friction is acting on can't ever be positive. It's probably a typo. – Aaron Stevens Apr 3 at 11:45
• ${}$ Which book? – Qmechanic Apr 3 at 12:45