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How Much Weight Can a Shopping Cart Hold?

By Rain Noe - July 28, 2016

in Materials

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One of the lessons I remember well from ID school was delivered by then-professor Bruce Hannah. Hannah was discussing the intelligent implementation of materials, using the bicycle wheel as an example.

He pointed out that the wire spokes are relatively inexpensive and individually quite weak, such that anyone in the class could hold one and bend it in half. But you take a bunch of them and attach them to a hub within a circular frame, and suddenly you have something absurdly, and affordably, strong.

The following GIF wasn't part of Hannah's lecture, but consider how well the spokes and rim are doing their job here:

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Another commonplace item that makes good use of wire is the classic shopping cart. Admittedly the underpinnings are actual tubes, but the design is still a fine example of exploiting the properties of economical materials to provide strength.

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So how much weight do you think one can hold? Has anyone ever warned you not to let your children ride on the front of a shopping cart, as they might break it? These folks here decided to stack weights into one to see if they could make it fail, and the end number is pretty darn surprising:

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I'd like to see how the plastic ones stand up.

Via The Awesomer

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Peter Enis

8 years ago

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The reason bicycle spokes are so strong isn't because there are so many of them. It's in how the forces are distributed, and when put in a circular shape, they all become basically tensile wires. There's never any force pressing them together or bending them. It's the same principle as in most modern stadium roofs.
The shopping cart on the other hand is a completely different construction which has, except for the material and the little shopping cart wheel, nothing to do with a bicycle wheel.
By connecting as many wires as there are horizontally in vertically, the basket becomes a sort of vierendeel construction. It only works because every single joint is rigid and forms a rectangle that doesn't change its shape. In an array, it becomes incredibly strong - the cart in the video breaks at the wheels, not the basket.
It isn't really the most material efficient construction, so thinking about it, it's kind of begging for a redesign…

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