Listen to Bill Hammack talking about the design of the aluminium drinks can and complete the task.

The objective of this is to prepare you for the next tasks by getting used to Bill’s voice.

Listen to the audio and complete each space with a number.

Every year nearly a half trillion of these cans are manufactured—that’s about per second, so many that we overlook the can’s superb engineering.

Let’s start with why the can is shaped like it is. Why a cylinder? An engineer might like to make a spherical can: it has the smallest surface area for a given volume and so it uses the least amount of material. And it also has no corners and so no weak points because the pressure in the can uniformly stresses the walls.

But a sphere is not practical to manufacture and, of course, it’ll roll off the table. Also, when packed as closely as possible only % of the total volume is taken up by the product. The other % is void space, which goes unused when transporting the cans or in a store display.

An engineer could solve this problem by making a cuboid-shaped can. It sits on a table, but it’s uncomfortable to hold and awkward to drink from. And while easier to manufacture than a sphere, these edges are weak points and require very thick walls.

But the cuboid surpasses the sphere in packing efficiently: it has almost no wasted space, although at the sacrifice of using more surface area to contain the same volume as the sphere.

So, to create a can engineers use a cylinder, which has elements of both shapes. From the top, it’s like a sphere, and from the side, it’s like a cuboid. A cylinder has a maximum packing factor of about % — not as good as the cuboid, but better than the sphere. Most important of all: the cylinder can be rapidly manufactured.

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