You approach the door of your friends house. What is the first thing you do before entering? Of course, you wipe your feet. You are a thoughtful visitor. Fortunately, there is a nice piece of carpet by the door to wipe your shoes. Too bad your caring comes at a price. After wiping your feet on the mat you reach out to touch the brass knocker on the door. A spark suddenly jumps between your hand and the metal. You feel an electric shock. Why do you think an electric shock occurs? An electric shock occurs when there is a sudden discharge of static electricity. Has this ever happened to you? You reached out to touch a metal doorknob and received an unpleasant electric shock? The reason you get a shock is because of moving electric charges. Moving electric charges also create lightning bolts. It is also the same reason electric current flows through cables and wires. 
When you approach a friends house, what is the first thing you do before entering?
Wipe my shoes