The soda-can tab is more than meets the eye.
In its resting state, the tab is what engineers call a "second-class" lever: The force you apply only moves one way, like a wheelbarrow.
When you lift the handles, the majority of the force falls on the wheel, in this case otherwise known as the fulcrum. This makes the load in the middle easier to move.
As Bill Hammack, YouTube's EngineerGuy and an engineer at the University of Illinois at Urbana-Champaign, explains in a recent video, pulling a soda-can tab exerts force on the rivet, which in this case is the load you want to move.
This lets you vent the pressurized can.
But something remarkable happens the moment you vent the can: The tab becomes a first-class lever, in which the force you apply changes direction around the fulcrum, like a seesaw.
"Part of the reason this clever design works," Hammack explains in the video, "is because the pressure inside the can helps to force the rivet up, which in turn depresses the outer edge of the top, until it vents the can and then the tab changes to a seesaw lever."
In other words, the wheelbarrow lever lets you exert great force with relatively little effort. In this case, it lets you create a vent from the rivet. The crack you hear is the pressure quickly equalizing. From there a simple seesaw lever breaks the seal itself.
Looking at the process from inside, you can see more clearly when the can vents.
This part is integral to the process, Hammack says, because if you tried to open the can just by pressing down on the seal without venting the can first, you'd need to make the tab enormous to fight back against the pressure inside the can. That would make it extremely expensive, not to mention oddly shaped and inefficient.
The actual design just goes to show that machines don't have to be complicated to be clever. Which is good news, considering that the tabs of yesteryear were as dumb as they were impractical.
Older soda and beer drinkers will remember the pull-away tabs that you'd either throw on the ground or drop into the can itself, hoping it wouldn't cut your lip when you went to take a sip. Thankfully, the tab got a full redesign in the 1980s.
Thirty years later, the design might just be the perfect way to crack open a Fresca.
