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Runners' Velocity with Earth Spin, Wood Rings

Hey, Matt: I do a lot of running, and while I was jogging through Balboa Park the other day, I started to wonder about my speed. I think I was running east, and since the earth rotates east to west, I was wondering if I’m running faster when I run east. When I run west the rotation works to my disadvantage. The globe is turning under my feet, and if it’s turning east, maybe I get a little advantage. Is there any way you can figure that ­out? — Running Man, Hillcrest

We kitted out the elves in jogging gear to answer this one. Grandma hunted around for elf-sized sports equipment and mostly came up with NFL onesies that were no help at all. But wouldn’t you know, she found an off-the-beaten-path fan store that had baby Lakers outfits, so the problem was solved. Tiny baggy bball shorts, tiny shirts. All the elves wanted to be Kobe, of course. So we divided the bunch in half, sent one jogging to the east, one to the west, hoping we’d get a good answer. Nobody’s come back yet, so Grandma’s gone off to look for them. I’m running out of time, so I’ll have to do my best without the field ­test.

So, Running, are you thinking that you’ll get to the finish line faster if you’re running east? We-e-e-ell, sorry. It doesn’t work that way. Your speed relative to a point on the earth isn’t helped at all by running east. Think of you flying in a plane and walking up to the cockpit. We’ll eliminate the ruckus you’ll cause with the flight crew and the FBI guys as you get near the pilots and they start looking for bombs in your socks. We’ll just say that the speed and direction of the plane has nothing to do with how fast you’ll reach the cockpit, right? You have to calculate your speed relative to something outside of the system you are in. Maybe the sun or a star — they’ll be good points of reference. So, are you running faster relative to the sun when you run ­east?

Assume that the earth is rotating on its axis just short of one time each 24 hours. That’s about 1000 miles per hour. (We’ll do a lot of rounding off here to make things easy.) As you move north on the globe, the relative rotation speed drops (it’s near zero at the pole). So, we’re here in San Diego, north of the equator. To find our speed, we take the cosine of the latitude of our city and multiply it by the equatorial speed. San Diego is roughly 32 degrees north latitude, which works out to 839 miles an hour. Here’s where it gets good: when you’re jogging east at, say, 3 miles an hour, you can add your puny 3 to 839, and in the end you’re running 842 mph relative to the sun. That’s the best we can do for you, Running Man. It’s not going to get you to the finish line any faster, but maybe it will keep your spirits up when you hit that ­wall.

Heymatt: I made some building blocks for my son out of some 2x2 pine I bought at Home Depot. I always heard that you could tell the age of the wood by counting the rings. Some of the blocks have 9 rings and others have tightly packed rings around 40. Can I accurately tell my son how old the wood is that these blocks came from? I know the sample in a 2x2 piece of wood is a tiny representation of the tree that it came from! What’s the deal, ­Matt? — Jack and Daddy in Oceanside

Well, Daddy is supposed to know everything, so we can’t start this early passing along bad facts. Yes, the blocks are only a small part of the total cross section of the pine trees that sacrificed their lives for your blocks. Each ring represents one year’s growth. But you only have a small bit of the whole tree, so you can’t really tell how old the tree was before it was cut down. You can say one tree was older than 9 years and the other was older than 40 years. You can say that it took 9 years to produce one block and 40 years to produce the second block. And you can also say the 9-ring block came from a tree that probably got more rain or nutrients or was a different variety of pine because it produced more wood between rings (that is, each year) than the 40-ring block. I can’t think of any other fancy facts you can use to wow Jack. But, once again, Jack’s daddy knows everything, so all’s well with the ­world.

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Hey, Matt: I do a lot of running, and while I was jogging through Balboa Park the other day, I started to wonder about my speed. I think I was running east, and since the earth rotates east to west, I was wondering if I’m running faster when I run east. When I run west the rotation works to my disadvantage. The globe is turning under my feet, and if it’s turning east, maybe I get a little advantage. Is there any way you can figure that ­out? — Running Man, Hillcrest

We kitted out the elves in jogging gear to answer this one. Grandma hunted around for elf-sized sports equipment and mostly came up with NFL onesies that were no help at all. But wouldn’t you know, she found an off-the-beaten-path fan store that had baby Lakers outfits, so the problem was solved. Tiny baggy bball shorts, tiny shirts. All the elves wanted to be Kobe, of course. So we divided the bunch in half, sent one jogging to the east, one to the west, hoping we’d get a good answer. Nobody’s come back yet, so Grandma’s gone off to look for them. I’m running out of time, so I’ll have to do my best without the field ­test.

So, Running, are you thinking that you’ll get to the finish line faster if you’re running east? We-e-e-ell, sorry. It doesn’t work that way. Your speed relative to a point on the earth isn’t helped at all by running east. Think of you flying in a plane and walking up to the cockpit. We’ll eliminate the ruckus you’ll cause with the flight crew and the FBI guys as you get near the pilots and they start looking for bombs in your socks. We’ll just say that the speed and direction of the plane has nothing to do with how fast you’ll reach the cockpit, right? You have to calculate your speed relative to something outside of the system you are in. Maybe the sun or a star — they’ll be good points of reference. So, are you running faster relative to the sun when you run ­east?

Assume that the earth is rotating on its axis just short of one time each 24 hours. That’s about 1000 miles per hour. (We’ll do a lot of rounding off here to make things easy.) As you move north on the globe, the relative rotation speed drops (it’s near zero at the pole). So, we’re here in San Diego, north of the equator. To find our speed, we take the cosine of the latitude of our city and multiply it by the equatorial speed. San Diego is roughly 32 degrees north latitude, which works out to 839 miles an hour. Here’s where it gets good: when you’re jogging east at, say, 3 miles an hour, you can add your puny 3 to 839, and in the end you’re running 842 mph relative to the sun. That’s the best we can do for you, Running Man. It’s not going to get you to the finish line any faster, but maybe it will keep your spirits up when you hit that ­wall.

Heymatt: I made some building blocks for my son out of some 2x2 pine I bought at Home Depot. I always heard that you could tell the age of the wood by counting the rings. Some of the blocks have 9 rings and others have tightly packed rings around 40. Can I accurately tell my son how old the wood is that these blocks came from? I know the sample in a 2x2 piece of wood is a tiny representation of the tree that it came from! What’s the deal, ­Matt? — Jack and Daddy in Oceanside

Well, Daddy is supposed to know everything, so we can’t start this early passing along bad facts. Yes, the blocks are only a small part of the total cross section of the pine trees that sacrificed their lives for your blocks. Each ring represents one year’s growth. But you only have a small bit of the whole tree, so you can’t really tell how old the tree was before it was cut down. You can say one tree was older than 9 years and the other was older than 40 years. You can say that it took 9 years to produce one block and 40 years to produce the second block. And you can also say the 9-ring block came from a tree that probably got more rain or nutrients or was a different variety of pine because it produced more wood between rings (that is, each year) than the 40-ring block. I can’t think of any other fancy facts you can use to wow Jack. But, once again, Jack’s daddy knows everything, so all’s well with the ­world.

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Comments
5

Matt, about Running Man's observation that "the earth rotates east to west."

Hmm. In that case, care to explain why the sun rises in the east?

July 23, 2010

The planet Earth indeed rotates counter clock-wise, West to East. Nice catch, Grok.

July 23, 2010

"duhhhhh, whatever"

July 25, 2010

RefrideGringo said: "The planet Earth indeed rotates counter clock-wise"

Not according to the Australian I work with!

Aug. 4, 2010

Those Australians do everything different! He's probably just confused because up here we can't use the Southern Cross as a point of reference ;)

Aug. 4, 2010

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