# Hooke's Law - no duh

I’ve always wondered why Hooke’s Law on elasticity is considered noteworthy. It seems awfully close to self-evident. Pull twice as hard, the thing stretches twice as much. Clearly, I’m missing something centrally important in his observation. What is it about that notion such that it has gained such an important place in the pantheon?

There are lots of things that people “knew” until someone sat down and ran some experiments. Heavy things obviously fall faster, for example. There’s no obvious reason why spring compressibility should be linear, even as a first approximation. Lots of things are exponential in nature.

It isn’t self-evident, because many elastic materials don’t follow it. A rubber band, for instance, has a force-stretch curve that’s, well, curved, instead of the straight line of Hooke’s Law: The more you stretch it, the greater the needed increased force. It happens to be true, or close to it, for many different situations, but that’s why it’s useful, not why it would not be useful.

And it happens to have a relatively simple solution, too, so it allows us to model real world situations with a clean, simple equation that is fairly accurate in a number of situations.

Hooke was a really clever guy. Up there with Newton in achievement, if not in self publicity. He got that "all bodies having a simple motion, will continue to move in a straight line, unless continually deflected from it by some extraneous force, causing them to describe a circle, an ellipse, or some other curve. 3. That this attraction is so much the greater as the bodies are nearer. As to the proportion in which those forces diminish by an increase of distance" before Newton found a proof.

Hookes law was most important for the development of an accurate timepiece that could be used for navigation.

And he did all this while captaining a pirate ship! Talk about a polymath.

Einstein was a patent clerk. Not nearly as exciting as captaining a pirate ship, but both careers probably had a lot of free time just the same.

…one-handed!

And ran a bagel restaurant chain.

I hear it’s his brother that does all the work…

And I never got how the spring constant gets to be called a “constant” and not a “value” or “number.”

It’s far worse then calling Pluto a planet.

It has a heck of a lot more right to that name than Hubble’s constant does. Barring extraordinary circumstances, the spring constant of a spring doesn’t change.

Well not for a particular spring it doesn’t.

But of course it does change depending on what spring is being considered. So it’s a constant that is…variable.

As opposed to the Big G gravitational constant for eample, which doesn’t vary as far as I know.

At least that’s the kind of thing I thought **Aquadementia **was getting at.

But now that I think about it, I’m not sure what you mean about the Hubble constant. Is it the imprecision in our measurement of it, or something else?

[Burton Guster]Did you hear about Pluto? That’s messed up, right?[/Burton Guster]

Yep. A name is easuer is remenber than an equation, and a persons name is easier to remember than some kind of verb thing.

I don’t have to decide if it’s an important relationship or an important man: it’s a relationship, so it has a name, and the name is the name of a person.

I could argue that calling it the ‘spring law’ would be more (or less) helpful, but I don’t think that’s the important central point.

It’s the fact that it’s constantly changing. In fact, in the simplest models which include it (which don’t accurately describe our Universe, but which make for a nice toy model), the Hubble “constant” is just the reciprocal of the age of the universe. Nobody would ever dream of calling an age a “constant”, would they?

Right - so what’s the big deal about it? I can’t discern an answer to my question here.

Because something being true isn’t a big deal, until someone realizes that it’s true. Hooke found a pattern in reality that is very widely useful to know about. If you really want to question someone’s fame, ask instead about the Atwood machine: What’s so special about two weights hanging from a pulley?

Another example of a “law” that’s not really a law is Ohm’s Law. For many objects, it happens to be the case that if you double the voltage you apply to it, then twice as much current flows through it. But it’s not true for many objects, and if you apply enough voltage to any object the direct proportionality won’t hold anymore.

Actually, the law that Ohm came up with is about the relationship between the temperature of an object and its resistance. The familiar V = IR is just the definition of resistance, and the observation that resistance so calculated is often a constant (or close enough to it) is interesting, but doesn’t apply anywhere where Ohm’s actual law is relevant.