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Pop Can Stay-on tab

Bill uses slow motion video to show the ingenious engineering design of the apparently simple tab of a pop can.

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Transcript Now, I know there are thousand of complex electronic gadgets that dazzle with their engineering, but the design of this ... [opens pop can],.. stuns me. I love that sound.

Here's the key problem an engineer solved: How to make this tab with the minimum amount of material but which would work every time on the billions of cans made every year. It looks simple, but designing this tab took five years.

You see the tabs used to be removable. I recall as a kid walking on a beach and cutting my feet.

In response to this envirnomental hazard an engineer designed an ingenious way to get the maximum leverage from the smallest piece of metal by making the tab change from a second to a first class lever. Let's me show you what I mean.

Recall that the arrangement of three components - the fulcrum, the force and the load - determines the class of lever. A second class≈ lever pulls on the load in its middle with the fulcrum and force at each end. An everyday example is a wheelbarrow.

In a first class lever the fulcrum and the load change positions: The fulcrum in the middle and the load at the end ... this is like a seesaw.

Now let's look at how this applies to the tab on a pop can

The tab starts as a second class lever where the tip of the tap is the fulcrum and the rivet the load, but then changes the moment the can vents to a first class lever where the load now at the tip and the fulcrum the rivet.

From the side you can see clearly how the tab, when working as a 2nd class lever, lifts the rivet. In fact, part of the reason this clever design works 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 first class lever.

If you tried to simply force the scored metal section into the can using tab as a first class lever with the rivet as the fulcrum throughout you'd be fighting the pressure inside the can: The tab would be enormous, and expensive. I'm Bill Hammack, the engineer guy.