Whenever you buy a can of this delicious, yet corrosive sugar-water, you have to open it with its tab. I didn’t think much of the design at first as you simply have to pull from one side and it all but comes off in your hands. In engineering terms, the tab itself is a second class lever whose force only responds in one direction. But, despite all the simplicity, the tab is a masterwork of engineering to address a simple problem. Let us see how it works.
With the load in the middle, when we exert force, much of it falls on the fulcrum or the point where the tab is rotating. By exerting only a certain magnitude of the force, the rivet is pulled out or down and then we can enjoy our soda. In this case, the rivet is the load we are are trying to move since it is a permanent joint that we are breaking up on the soda can surface. But, the remarkable thing is that it doesn’t remain a second class lever as soon as the vent is opened. The reason is that once it gets opened, the fulcrum moves to the middle, and now it is a good old first class lever that produces turning action instead of translational action.
But no ordinary lever can be transformed so quickly. Part of the trick that makes it happen is the pressure inside the can that is greater than the atmospheric one, so it propels the tab upwards and thus making it a first class lever. In other words, first you have a wheelbarrow kind of lever where the force only results in one directional motion, and after the rivet is broken, it converts into a see-saw kind of lever. The crack you hear is, of course, the pressure equalizing inside the pressurized can.
I am sure all the readers won’t look at the can the same way ever again!
See this video for more:
[Via Tech Insider]