Why does double bagging groceries work? Isn’t the second bag carrying not only the load of the groceries but also the load of the bag?
In: Engineering
I would use nylon rope that could only lift 500lbs to lift 2,000lbs. How? I wrapped it around a few times. The weight would be distributed through each wrap. Meaning that each wrap was lifting less than 500lbs. But combined they lifted the 2000lbs.
Also, this was with a forklift. I’m not claiming that I lifted 2,000lbs by hand.
The idea is that both bags are the exact same dimensions, and so the stress will be halved on each bag, as well as the weight on each handle…the equivalent of a double thickness bag, with only half the weight as before on each handle. in practice, though, if the bags are not the exact same dimension, the entire system breaks down. just putting a bag inside of the same dimensions and not using its handles is nearly worthless (the slight thickening of the bag *might* prevent some brute stress tearing), and using the handle of bags of a different size is totally useless. The system only works when the two bags are extremely similar and you use all four handles.
Both sets of bag handles are pulling down on you, which means the weight is distributed between each bag more or less evenly.
The load is the first bag is negligible. Think of it like toilet paper – 1 ply is pretty weak, but 2 ply is stronger. A thicker bag will be sturdier than a thin one, everything else being equal.
Double bagging produces strengths in several ways. There’s the increased strength of the handles in supporting the weight, but a single bag usually can support the weight. Some items in the bag may be sharp, have corners or put more pressure in an area. These areas can burst out of a single bag. You are then stranded with some items broken and not enough pockets to carry the survivors. The extra bag is comforting insurance in most cases and disaster prevention in others.
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