I’m feeling rather random today. Usually I save my “random” posts for the fifth Friday of a month, if there is one. However, I was fairly serious on August 31, exhorting you to do your backups, so I have a random day coming to me. Besides, I don’t want to wait until November. So here you go—three little notes that don’t belong anywhere else. Enjoy.

SigFigs
Do you remember learning about  “significant figures” in science class? It’s the idea that being too exact can be a waste of effort.Or, to define it more precisely, significant figures are “spurious digits introduced, for example, by calculations carried out to greater precision than that of the original data, or measurements reported to a greater precision than the equipment supports.” One example would be using a tape measure to determine the length of your finger, then expressing the result in microns. Saying there are exactly 10,209, 347 House Sparrows is another example.

Could that concept apply here?

Pete was pouring his generic shredded wheat biscuits into his cereal bowl this morning when he noticed the “best used by” date on the box: July 09, 2019, at 2:53. One wonders if this is am or pm. Does this mean that at 2:54 the cereal suddenly becomes stale and tasteless? At least it isn’t an expiration date—we won’t be endangering our health if we consume the contents on July 10.

Speed of Sound
A friend told me, “When I lived in Florida, I used to time how long it took to hear thunder after seeing a flash of lightning, to find out how far away the storm was, but it doesn’t work here in Colorado because sound travels differently.”

My first inclination was to laugh (not a good way to keep the friendship!), but then I wondered—could this possibly be true? Before I gave her a hard time about her lack of scientific understanding, I’d better make sure I knew the facts. Here’s what I learned.

I figured that there are three major differences between Florida and Colorado that could potentially affect the speed of sound: elevation, humidity, and temperature. It turns out that elevation and humidity have no effect whatsoever. However, temperature does affect the speed at which sound travels.

The next question was, how much does the speed change? Is this something that we could notice when counting seconds after a flash of lightning? A quick search turned up a handy calculator, and I plugged in some numbers. Here are my results at both meters per second and miles per hour:

90 degrees F = 350.297 m/sec, 783.59 mph
50 degrees F = 337.311 m/sec, 754.54 mph
32 degrees F = 331.301 m/sec, 741.096 mph

Now let’s apply this to real life. When we want to know how far away the lightning is, we are usually thinking in miles, not meters, and seconds, not hours. So I converted my units. (Note that I applied the rule of significant figures here, lopping off the last 6 decimal points that Google provided.)

90 degrees F = .217 miles per second
50 degrees F = .209 miles per second
32 degrees F = .205 miles per second

These temperatures represent the extremes. Here in Colorado, thunderstorms happen during the warmer months, when Florida and Colorado are both hot. Florida probably feels hotter because of its higher humidity, but remember, humidity doesn’t matter in this case.

So, you see the lightning flash and begin counting: one thousand one, one thousand two, one thousand three…. and boom! Here comes the thunder. How far away is the storm? It takes about five seconds for thunder to travel one mile. Let’s say you get to ten. You divide by five, and the lightning hit about two miles away.

Now, remember those significant figures. First of all, the thunder doesn’t arrive all at once. You get a rumble that goes on for a little bit. Then, how accurate is your counting? Even if you’re used to 95 degree storms in Florida, and it’s only 85 degrees in Colorado, you could have to be accurate to a one-hundreth of a mile for the difference in temperature to matter. And that’s all in the noise.

Purring Cats
While we no longer have any pets, I spent most of my life owned by at least one cat. And if you hang around cats for very long, you realize that cats purr for a number of reasons. Yes, cats purr when happy; stroking their fur and scratching their ears is a surefire way to get a rumbling response. However, all my cats also purred at the vet—and I guarantee they were not happy to be there!

Cats also spend up to 80% of their lives snoozing. There are benefits—sleeping saves energy, and while our cats were very well fed, saving energy in the wild means you don’t have to hunt as much. Yet, lying around weakens bones.

So why do cats purr so much? Apparently, the low frequency of purring (between 25 and 150 Hertz) has health benefits. Low vibrations make bones denser—just what sleeping cats need to stay strong and fit.

These frequencies also seem to speed healing, especially of muscles and tendons, and to reduce pain and swelling around injuries. The next time I hurt myself, maybe I’ll forego the ice bag and try a purring cat instead.