The terms pressure and force are defined differently but may be defined as identical, if desired. I think the Newton force argument is specious because it doesn't account for area of impact. So pressures are more useful to know how much crunch something can provide, and they are the bite-force proper divided by this area of teeth or mouth or so that it acts over. (Meanwhile a string almost can't be compressed it squirms out of the way when you try. So it's much more breakable under tension than under compression. These material properties are often different! A good example is concrete when you're pushing it together you're usually trying to push rocks into other rocks, and that is very difficult when you're pulling it apart you're usually trying to pull apart the cement that binds those rocks, which is much easier. Now if we are talking about whether a predator's teeth can crunch your bones, it turns out that a bunch of similar physics is in play and your bones will crunch at a particular stress - just where the strings were in tension the bones being crunched are in compression. Also we find out that the material breaks at certain stresses. And then we find that materials actually have a stress-strain graph which we can plot, and this result will hold for other lengths and other cross-sectional areas. So to get actual "material properties" we have to divide the stretch by the rest length - this is called the "strain" of the material - and we have to divide the force by the cross-section area - this is called the "stress" of the material. What changes is that if we measure the distance it stretches, between its unladen and loaded length, generally half the string will only stretch half as far. Half as long, it will hold about the same weight - a little more due to the mass of the string that's now missing - before breaking. This is not in general true if you make the string half as long. So two strings hold twice the weight, three strings hold three times the weight, and so on. What would you expect from two strings side-by-side? Well, we could hang another weight, exactly as heavy as the first, from that other string: but again, any heavier on either string and you'd expect it to break. Suppose I hang a weight from a string, and the weight is just heavy enough that any heavier a weight would break the string.
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