actin out

Quick: what’s the difference between an ‘amu’ (atomic mass unit) and a ‘Da’ (Dalton)? Answer: Nothing. They both represent one-twelfth of the rest mass of an unbound carbon-12 atom in its nuclear and electronic ground state, a.k.a 1.66×10−27 kg. This is very slightly less than the mass of a proton or a neutron (approximately 1.67×10-27 kg). When first invented, the Dalton was intended to be a fundamental unit such that one hydrogen atom had a mass of one Dalton. Helium would be two Daltons, lithium would be three Daltons, etc. Of course, then we realized that every atom had different numbers of protons, neutrons and electrons, which mean that there was no simple universal mass. It would be so much easier to memorize if everything on the periodic table was a simple multiple of a fundamental quantity.

vis-co-e-las-tic-i-ty ex-pi-al-ido-cious or… what can’t you do with carbon nanotubes?

Some words are just so much fun to say. My father claimed that, as a child, I was inordinately amused by long Latin words from his legal texts.
But you must admit that viscoelasticity is just a cool word. Like most words, you can break it down into its component parts: viscous and elastic. And like most things in physics, it’s almost always “beyond the scope of the course”. You can talk in a limited way about elasticity (spring constants) and sometimes you’ll learn a little about viscosity, but viscoelasticity consistently fails to make it into most introductory physics books. That’s too bad because it’s not only a fun concept, it is a useful concept.

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