## Tuesday, May 24, 2016

### Playground Physics

Playgrounds are a great place to learn some basic physics. Or at least they were 50 years ago, before the safety mavens moved in and rebuilt everything in plastic and foam rubber. Take a look at this old seesaw:

The physics lesson is right in the center: the seesaw rested on an open pivot, so that you could just lift it up and move it, making one side shorter than the other. This was a perfect illustration of a lever -- a lighter kid on the longer end could easily balance against a heavier kid on the shorter end. At least until one of them jumped off, sending the other crashing to the ground. But it was the movable pivot that doomed this particular type of seesaw. You can see how easy it would be to get your fingers crushed in the center. I never actually saw this happen, but we all lived in dread of the possibility.

An even more interesting physics demonstration was the old-fashioned merry-go-round:

The game here was to push the merry-go-round as fast as possible, until centrifugal force almost flung everyone off. Disclaimer: we teach all of our college freshmen that there's really no such thing as centrifugal force. The force actually points inward, and it's called "centripetal force." But if our students go on to a more advanced class, they learn that there really is such a thing as centrifugal force, but it's a "fictitious force" --  a force that only appears in an accelerating frame of reference. So when you're flung off the merry-go-round and scrape your legs while sliding across the concrete, you can comfort yourself with the fact that it was only a fictitious force that threw you across the playground.

## Thursday, May 19, 2016

### Galaxy Quest

I watched Galaxy Quest again the other night. It's a hilarious spoof of Star Trek -- a group of washed-up actors from a cancelled science fiction TV series are mistaken for the real thing by aliens who have intercepted their TV broadcasts and who need their help to defeat their ruthless foes.

## Wednesday, May 11, 2016

### Chipmunk Delenda Est

I am engaged in an ongoing war with a family of chipmunks that has taken up residence in a narrow strip of ground between my house and our outdoor fish pond. They are perilously close to burrowing through the pond liner, unleashing a thousand gallons of water against the base of my house.

While the chipmunks and I are evenly matched intellectually, I am thus far in the lead, 2-0. But my battle against the chipmunks led me to this scenario:

Imagine that the doorbell rings, and you go to the front door to discover an unexpected package from Amazon. The box is strangely wrapped, and some of the words are misspelled, but you can see that it's stuffed full of money -- some of the cash is leaking out of rips in the cardboard. So you lean over to pick up the box and... thwack! Revenge of the chipmunks.

## Friday, May 6, 2016

### To the Stars, on a Ray of Light

I gave up on dreams of interstellar travel a long time ago. I outgrew them, just as I outgrew the Tooth Fairy and the Easter Bunny. And then last month, along came this paper by Philip Lubin from the University of California at Santa Barbara, claiming that interstellar travel is feasible with existing technology.

## Wednesday, May 4, 2016

### Before there was the Internet, there was....Semaphore!

Boy Scouting and I didn't really get along too well. I hated camping, and I thought nature was best viewed from the comfort of a hotel room. None of this was helped by the fact that my Boy Scout Troop was the most amazing collection of losers and goofballs ever assembled under the Boy Scout umbrella. At our local camping competitions, we would invariably finish last. Our scoutmaster became so enraged at one of our meetings that he threatened to walk out and never come back if we didn't settle down. We took this as the usual empty adult threat (did your dad ever really turn the car around and drive back home on the way to a family vacation?) So we kept up our antics. Much to our surprise, our scoutmaster did walk out of our meeting, got into his car, and drove away, never to be seen again. Thus ended my career in Scouting.

But I did learn a few worthwhile things in the Boy Scouts. I can tell the difference between venous bleeding and arterial bleeding (the difference is that arterial bleeding means you're going to die). I can identify poison ivy -- most of the time, anyway. And best of all, I learned semaphore.

Semaphore was an early version of the internet. Packets of information, called "letters" were encoded as positions of two signal flags and transmitted through the air over literally tens of yards. Transmission rates of 1-2 bytes per second were possible.  (Quiz: with two signal flags, and eight different flag positions, how many different letters can be encoded? The two flags cannot occupy the same position).

Semaphore plays a role in L. Sprague de Camp's classic novel, Lest Darkness Fall. The protagonist finds himself hurled back in time to the last days of the Roman Empire, and he sets about trying to stave off its collapse. It's an interesting idea -- what are the "doable" technological improvements you could introduce to the ancient world? He starts with Arabic numerals and eventually introduces a system of cross-country semaphores to allow for rapid communication across the empire. But this raises an interesting question -- why didn't ancient civilizations, or for that matter, any pre-telegraph civilizations, use systems of semaphore towers?