Re: Questions (Space)

FennelGiraffe <sraarytvenssr@xxxxxxxxxxxxxxxxx> wrote:
Tina.Hall@xxxxxxxxxxxxxxxxx (Tina Hall) wrote
FennelGiraffe <sraarytvenssr@xxxxxxxxxxxxxxxxx> wrote:
Tina_Hall@xxxxxxxxxxx (Tina Hall) wrote

Well, I know that it is so (the last line quoted here), but with the
way you phase it above (that last line), I would have to insert
some route travelled, and there the foot, bike, and car are
incompatible.

OK. "Speed" really doesn't mean the same thing to you as it does to
me (and I think most other people). You have route and maybe some
other stuff tangled up in there. That's going to be a problem. I'll
have to think about how to get around it.

I get the feeling that it's also spread out across different drawers,
and different things someone says pluck out the association from any one
of them, not always the same one. (I'm worrying that the 'plucking out'
choosing is kind of random, accidentally. So something might hit home
with association A, but next time it comes up it meets association B and
doesn't fit.)

And my mind defaults to 'gets to <certain point> quicker', rather
than 'gets farther'.

That's just as valid a way to look at it. Actually, most of the
everyday ways we care about speed are "how long does it take to get
there". Even races are a set distance and the winner is the one who
needs the least time to get there.

The problem is that the way we *measure* speed -- kilometers per
hour, etc. -- is the other way around. It's based on asking how much
distance can be travelled in a set time. Comparing two speeds is
expressed in terms of which one can go farther in the same time.

Well, I know that a higher number means faster, but the numbers
themselves don't tell me anything.

I know how much 5 minutes are. I can (very badly) estimate how much 100m
are (I could guess anything from around 20m to 500m to be 100m, I'm just
very bad at estimating that). Easier is 2m, I know how much 2m are.

I don't know how fast 10km/h are. I just know it's slower than 11km/h.
But the whole thing isn't tangible, in a 'to touch' sense.

That makes sense (but I just see the numbers, my mind blanks out
the km/ h).

It's the ratios you were talking about above. 70 km/h is exactly
the same thing as 70km:1h.

You're right. (I'm somewhat surprised.)

Yea! Progress.

:)

I guess it comes in handy elsewhere, though.

But then, you decide on 'relative to a certain point' (the ocean
in this case). You could just as well just look at the bug, or in
the other direction; include earth turning and moving around the
sun and the sun moving in the galaxy.

Exactly.

And?

*Everything* is relative to some point -- in any particular
discussion that point is called the "frame of reference"[1]. People
often assume that particular kinds of discussions imply particular
frames of reference. Of course, to be thorough, we should make it
clear every time.

So speed is relative to a point. But that doesn't help my image of
'speed'. (Or then, velocity. The speed in a certain direction thing.)

When people are talking about everyday sorts of problems involving
moving around on the surface of the Earth, they don't usually bother
to say that they only care about motion relative to one particular
spot on the surface of the Earth (usually the spot they started
from).

When people are talking about planets and other bodies in a solar
system, or spacecraft traveling from one planet to another in the
same solar system, everything is usually expressed relative to the
center of the sun.

Why do they see it relative to the sun when they, for example, send a
probe to Mars? Does that (x,y,z) thing come in there?

When people are talking about satellites orbiting a planet, the
center of that planet is the most common frame of reference, but once
in a while people use the center of the sun, instead.

The example above could also be looked at from the bug's frame of
reference. Then he's not moving at all, but everything around him is.

Reminds me of some funny idea someone had while sitting in a train.
(Someone moving the houses past the train.) I think I've always thought
that a bit silly. Like I walk away from a person and then claim he left.
It's just not true.

And that's not just court truth. I think it does matter who's spending
the energy to do the moving.

And inside the train, I, personally, am not moving, but the train is
transporting me, so I'm moved anyway.

But I wonder whether it would cost me (minimally) more, or less, energy
to walk forwards, or backwards. (Just a thought, I'd like to know for
sure.) That's counting train and earth and whatever forces are involved,
not just myself and the floor of the train. The same should then apply
to an escalator.

[1] More properly, I should say it's the zero point, the "origin", of
the frame of reference.

Zero point sounds like a cool term for <something> in a sci-fi story. :)
(I think anything with 'zero' could sound cool.)

But that's all the term does for me.

--
Tina
WIP: Space: 2666 words
WISuspension: Seasons & Elements trilogy | Magic Earth series
Posted to Usenet newsgroup rec.arts.sf.composition.

.

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