MitD XIII: Learning is happening

[Grey_Wolf_c]

Double height means eight times mass, all other things being equal.

They must not be. It turns out that one of the best predictors of adult human heights is 2*(height when 2 years old). Healthy weight at 2 years old is ~12.5 kg (google tells me). 8 times that is 100 kg, which is a bit over healthy adult human weight. So I'm guessing that while it is mostly true that all things stay roughly the same, not all of them do, and proportions are not quite the same.

But, on the other hand, remarkably close, all things considered. Good rule of thumb, if nothing else.

Grey Wolf

[Peelee]

They must not be. It turns out that one of the best predictors of adult human heights is 2*(height when 2 years old).

Grey Wolf

Source? My little dude is slowly coming up on 2, and I'd love r8 be able to decently predict how big he's gonna get!

100 kg, which is a bit over healthy adult human weight.

Grey Wolf

A bit?!? I'm clocking in a little over 90 and I have a very round and poke-out-my-shirt belly! I'm concerned about being too fat, and with good reason!

[hamishspence]

Might depend on how much extra bone thickness is needed for larger creatures.

Is an elephant 6 ft tall at the shoulder, typically 1/8 the weight of of an elephant 12 ft tall at the shoulder - or does the extra size tend to mean proportionally thicker bones and the creature being slightly overweight for its size?

Or does the reverse tend to apply - with "weight-lightening air sacs" (for example, in big dinosaurs) making a 100 ft sauropod significantly less than 8x the weight of a closely related 50 ft sauropod?

[Grey_Wolf_c]

Source? My little dude is slowly coming up on 2, and I'd love r8 be able to decently predict how big he's gonna get!

A couple of different pediatricians. I took them at their word. You may want to ask yours if they agree and, if so, why.

A bit?!? I'm clocking in a little over 90 and I have a very round and poke-out-my-shirt belly! I'm concerned about being too fat, and with good reason!

OK, fair enough, it's about 33% off, which is more than just a bit (this assumes 176 cm of height, and a target weight of 75 kg)

Or does the reverse tend to apply - with "weight-lightening air sacs" (for example, in big dinosaurs) making a 100 ft sauropod significantly less than 8x the weight of a closely related 50 ft sauropod?

I would not expect the formula to apply even between closely related creatures, since scale differences, as you point out, will inevitably quickly select for different weight-related characteristics.

Grey Wolf

[D.One]

Source? My little dude is slowly coming up on 2, and I'd love r8 be able to decently predict how big he's gonna get!

My mother says my "2-years prediction" was pretty on the spot. Still waiting to see how it will turn out for my own children.

[Peelee]

A couple of different pediatricians. I took them at their word. You may want to ask yours if they agree and, if so, why.

Grey Wolf

Nah, I generally accept when you say stuff is backed up, I just wanted to see if there was any metaphorical small print.

[Darth Paul]

A bit?!? I'm clocking in a little over 90 and I have a very round and poke-out-my-shirt belly! I'm concerned about being too fat, and with good reason!

What's that in American? Because I have the feeling I'm around... maybe 120-130? I don't feel like getting the calculator out...

I know I'm 20 stone, because there's a converter on Google. That makes me feel skinny, because it's only 20 of whatever that is.

[hamishspence]

What's that in American? Because I have the feeling I'm around... maybe 120-130? I don't feel like getting the calculator out...

20 stone is 280 pounds is 127 kilos.

[Darth Paul]

20 stone is 280 pounds is 127 kilos.

I know what I weigh in American, thanks, I was wondering what the 90 was, for comparison purposes.

[hamishspence]

90 kg is 198.4 pounds is 14 stone 2.4 pounds.

[Darth Paul]

90 kg is 198.4 pounds is 14 stone 2.4 pounds.

So Peelee is a skinny little sod, by comparison. He can take comfort that people like me are around!!

[Joerg]

They must not be. It turns out that one of the best predictors of adult human heights is 2*(height when 2 years old).

Is that for male or female children or both? I imagine there's not much height difference in two years olds, but there's a significant difference in adults.

Healthy weight at 2 years old is ~12.5 kg (google tells me). 8 times that is 100 kg, which is a bit over healthy adult human weight.

Same question.

[Peelee]

So Peelee is a skinny little sod, by comparison. He can take comfort that people like me are around!!

Look, that's fat for 5'10! I take no comfort that others may be more so, I've still just a big gut hanging out! I do hope to fix it, also.

[Grey_Wolf_c]

Is that for male or female children or both? I imagine there's not much height difference in two years olds, but there's a significant difference in adults.

Both, surprisingly.

Grey Wolf

[Crusher]

Both, surprisingly.

Grey Wolf

In my experience, its arguably close, but part of that is because adult humans mostly fall into a relatively narrow range. For example, my daughters at age 2 were 33 1/2" and 34 1/2" inches tall, suggesting they'd be approximately 5'7" and 5'9" when fully grown. The taller (and older) topped out around 5' 4 1/2", missing her prediction by 4 1/2". That's pretty accurate in absolute terms, but given that her probable height range was between 5'2" and 5'10" (looking at American women overall), it was actually a pretty bad predictor. She's still a bit bitter about it.

The younger one is probably still growing but she's currently 5' 2 1/2" so if she stops growing now, she'll miss by almost exactly the same amount (at the moment, she's a little more accepting of her probable height fate). Which is about what I actually expected, given that I'm slightly below average height (for American men, 5'8") and more importantly stopped growing at around age 14 (I was decently tall for a 14 year-old, but rapidly lost ground to other folks). My wife also stopped growing young, suggesting the kids would probably also stop growing young.

[terodil]

For example, my daughters at age 2 were 33 1/2" and 34 1/2" inches tall, suggesting they'd be approximately 5'7" and 5'9" when fully grown. [and a lot more measurements in weird units]

And the headaches you just got when trying to double the figures, kids, are why you don't use imperial. (Also, this.)

OK, to increase the helpfulness index of this post, here's the translation into useful numbers:

In my experience, its arguably close, but part of that is because adult humans mostly fall into a relatively narrow range. For example, my daughters at age 2 were 85cm and 87.6cm tall, suggesting they'd be approximately 170cm and 175cm when fully grown. The taller (and older) topped out around 164cm, missing her prediction by 11.4cm. That's pretty accurate in absolute terms, but given that her probable height range was between 157.5cm and 177.8cm (looking at American women overall), it was actually a pretty bad predictor. She's still a bit bitter about it.

The younger one is probably still growing but she's currently 159cm so if she stops growing now, she'll miss by almost exactly the same amount (at the moment, she's a little more accepting of her probable height fate). Which is about what I actually expected, given that I'm slightly below average height (for American men, 173cm) and more importantly stopped growing at around age 14 (I was decently tall for a 14 year-old, but rapidly lost ground to other folks). My wife also stopped growing young, suggesting the kids would probably also stop growing young.

[Peelee]

And the headaches you just got when trying to double the figures, kids, are why you don't use imperial. (Also, this.)

I don't know anyone who uses imperial. I know a bunch of people who use American Customary Units.

[Crusher]

And the headaches you just got when trying to double the figures, kids, are why you don't use imperial. (Also, this.)

OK, to increase the helpfulness index of this post, here's the translation into useful numbers:

Oh, sure. *Anyone* can do math in base10. When you want a real challenge, come back and work in a system where your base changes arbitrarily as you move up in units. From 10 to 12 to the rarely used 3 to 5280. Believe me, it’s a joy.

They actually started shifting to metric when I was a kid, but dumber heads prevailed.

“Wait how many inches are in a mile again?” “Odin’s knees, lad. No one cares.”

[Jasdoif]

Oh, sure. *Anyone* can do math in base10. When you want a real challenge, come back and work in a system where your base changes arbitrarily as you move up in units. From 10 to 12 to the rarely used 3 to 5280. Believe me, it’s a joy.

They actually started shifting to metric when I was a kid, but dumber heads prevailed.

“Wait how many inches are in a mile again?” “Odin’s knees, lad. No one cares.”

I dunno....When I see stuff like "2 tablespoons (28.3g)", I kinda wonder how much is cultural inertia and how much is the advantage of domain-specific units at work.

[LadyEowyn]

I dunno....When I see stuff like "2 tablespoons (28.3g)", I kinda wonder how much is cultural inertia and how much is the advantage of domain-specific units at work.

That’s just silly. You have to be willing to round (say, 30g).

Also, that’s a weird recipe if it converts volume (Tbsp) to mass (g). It should convert to mL.

[hamishspence]

Also, that’s a weird recipe if it converts volume (Tbsp) to mass (g). It should convert to mL.

Maybe it uses a a certain density as a fairly typical one for conversions?

1 tablespoon = 3 teaspoons = 1/2 ounce = 14 grams

seems to be the main conversion factor.

[Jasdoif]

Also, that’s a weird recipe if it converts volume (Tbsp) to mass (g). It should convert to mL.

That was my first thought; but then I realized that something like flour, which tends to spread a lot, would be extremely aggravating to measure by volume if you were forced to use a partial container. A weight/mass value would be far more convenient in that scenario.

[Ruck]

I don't know anyone who uses imperial. I know a bunch of people who use American Customary Units.

You're getting stiffed not getting a 20 oz pint at the pub, I tells ya!

[Qwertystop]

That was my first thought; but then I realized that something like flour, which tends to spread a lot, would be extremely aggravating to measure by volume if you were forced to use a partial container. A weight/mass value would be far more convenient in that scenario.

Weight is indeed the most accurate way to measure flour, but in practice more people have measuring cups than kitchen scales and most recipes (for home cooks) are written to match.

[lio45]

Double height means eight times mass, all other things being equal.

Double height can be anywhere between 2x mass and 8x mass, depending on how exactly other factors change as you're doubling the height.

Take a cube that's 1m by 1m by 1m.
(1' x 1' x 1' for Americans, if you prefer, not that the unit we pick matters.)

As you pointed out, you can "double its height" by increasing the dimensions proportionally in every of the three dimensions, where the result is a first level of four original cubes arranged in a square, and an identical second level of another four original cubes (forming a 2m x 2m x 2m cube).

But you can also "double its height" by putting a second cube on top of the first, resulting in a 1m x 1m x 2m "tower" (a rectangular prism).



... I guess where I was going with this is that if we take a random creature, and a child/baby is half the "size"/height of an adult, then mass is going to be somewhere between half and one eighth; these work decently as extreme boundaries, and a realistic estimate would likely be somewhere in the middle.

[hamishspence]

... I guess where I was going with this is that if we take a random creature, and a child/baby is half the "size"/height of an adult, then mass is going to be somewhere between half and one eighth; these work decently as extreme boundaries, and a realistic estimate would likely be somewhere in the middle.

True - but unless the baby's proportions are radically different from the adult's, it's likely to skew toward the 1/8 end of the scale.

[Vendanna]

Did anyone here also ate tacos to celebrate 5 de mayo, like in that strip with the mitd? :D

[Jasdoif]

Did anyone here also ate tacos to celebrate 5 de mayo, like in that strip with the mitd? :D

Burritos and a taco salad, here.

[Dr.Gunsforhands]

A new grocery shop had its grand opening on my street today! There was cake and gelatin, and I bought some tortillas and apple soda.

[Wizard_Lizard]

and then there is me wighing about 50kg