Three things are worth noting about frictional forces: these fundamental points will help you to understand friction as a force, answer questions from the friction chapter and solve numerical problems based on friction. Here are the points:

- The smaller µ is, the more slippery the surface. For instance, ice will have much lower coefficients of friction than Velcro. In cases where µ=0 , the force of friction is zero, which is the case on ideal frictionless surfaces.
- The coefficient of kinetic friction is smaller than the coefficient of static friction. That means it takes more force to start a stationary object moving than to keep it in motion.
- Frictional forces are directly proportional to the normal force. That’s why it’s harder to slide a heavy object along the floor than a light one. A light coin can slide several meters across a table because the kinetic friction, proportional to the normal force, is quite small.