So I was looking at another answer and it indicated that polar bears have a bite of 1200PSI.
This seems crazy, even a small force crushing something between the edges of two teeth would generate a huge PSI value.
Why do they use PSI, shouldn’t it be lbs-force (well OK it should be newtons, but that’s another issue)?
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You’re right that it’s a really sloppy use of terminology/units, but there’s valid reasons to care about both the pressure (psi or whatever) *and* the force (lbf or whatever).
Your ability to cut through materials, which is what we usually do with teeth, is almost entirely related to pressure. Whether you’re crushing (compressive strength…molars) or shearing (shear strength…incisors) or warping (yield strength…some of each), what matters is that the teeth apply more pressure than the relevant material property. So you can directly compare bite “force” in pressure to the compressive/shear/yield strength of the material you’re biting and have a reasonable estimate for whether your teeth will do anything useful to the material.
But teeth have another important function for *some* animals…they’re a way of grabbing and tearing things. In that case, pressure isn’t really that relevant, you don’t need to cut the material with your teeth, you just need to hold on to it. But the *force* you can apply is really important. A mouse with a bite “force” of 20,000 psi can totally cut my skin but isn’t going to pull my finger off because their bite force is probably only a few lbf. On the other hand, something with big blunt teeth (moose?) might only be able to put down 500 psi bite “force” but they can easily tear my arm off because their total bite force is probably up in the thousands of pounds (I am speculating on values here, don’t overthink the numbers, the point is that pressure and force are good for different things when biting).
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