The tab on top of a soda can is more complicated than it may seem. First, the tab acts as a second class lever. a second class lever is a lever in which the fulcrum is at one end and the load is in the middle. the load is the point where the tab is attached to the can. In a second class lever, the force only moves up. One example of a second class lever is a wheelbarrow. The rivet in the middle of the can is pulled up until it reaches a point where a small crevice opens up. once this crevice appears, the tab immediately turns into a first class lever. a first class lever is when the fulcrum is in the middle, and the load is on one end while the force is on the other end. an example of a first class lever is a see saw. the first class lever is used to push the top down into the can, allowing you to drink from it. The crevice in the can is very important in the opening process. The can has so much pressure that just pushing down on the seal would require a tremendous amount of force. cans would need a very long tab, which would be impractical. the crevice releases pressure in the can.
skip to 9:13 for the stuff about the can opener.