1. We can reduce friction by using table and block with smooth surfaces.
2. There are three types of friction: potential friction, kinetic friction and static friction.
3. Static friction tends to prevent a slipping.
4. The friction of impending slip is denoted by F0.
5. The force of friction is equal to the total force pressing one surface against another.
6. The sliding friction force decreases because of the replacing of sliding friction by rolling friction.
Read the text and answer the questions: Why does every machine waste energy? What is the efficiency of machine? What is the simplest form of machine? What is the actual mechanical advantage? What is the principle of the pulley operation? jackscrew operation?