[meteorite-list] MIND BLOWING

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Sat, 14 Jul 2007 21:26:55 -0600
Message-ID: <042201c7c690$05074020$2721500a_at_bellatrix>

Hi Sterling-

If you give it some more thought, you'll probably figure out that the
potential energy of wind scales as the cube of velocity, not the square.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
To: "Pete Pete" <rsvp321 at hotmail.com>; <mlblood at cox.net>;
<meteorite-list at meteoritecentral.com>
Sent: Saturday, July 14, 2007 6:28 PM
Subject: Re: [meteorite-list] MIND BLOWING


> Hi, Pete, Michael, List,
>
> The first thing I thought of was... Mars, just like
> you. But the air thereabouts is awful thin. I guess
> it's calculator time.
> The density (or pressure) of the Mars atmosphere
> is only about 1/100 of the Earth's. How a wind "feels"
> to an object in its path is dependent on the density of
> the wind (the number of molecules per unit volume)
> and the velocity of the wind. The momentum of the
> wind is the density (really the mass of the molecules in
> the wind added together) times the velocity of the wind.
> So, an object on Mars will encounter wind with 1/100
> the momentum of wind on the Earth traveling at the
> same velocity. That means the wind on Mars has to be
> traveling a 100 times faster than the wind on Earth to
> have the same momentum.
> However, the kinetic energy content of the wind is
> dependent on the velocity of the wind squared (or
> E = (M x V x V)/2, so the wind on Mars only has
> to travel about 10 times as fast to make up for the
> difference in density.
> Mars atmosphere is mostly CO2, a heavy molecule.
> It's not the same as the Earth's atmosphere. The details
> are the density of the atmosphere at the surface of Mars
> is only 81 times smaller than Earth's. Therefore, to "feel"
> the force of a breeze on Mars of the same force as on Earth,
> we would require 9 times the wind velocity (square root
> of 81). For example, to "feel" a light breeze of about 10
> miles/hr on Earth, would require "hurricane speed" winds on
> Mars of 90 miles/hr.
> It's obvious from the video that these walkers require
> as much wind as they can get, here on Earth, or they wouldn't
> be walking on a windy beaches! Here's another complication.
> The gravity on Mars is only 38% of Earth's, so it only takes
> 38% of the force to lift a "foot" up. The walker only "weighs"
> 38% of what it would on Earth. Maybe a "Mars Walker" would
> only require a wind about 5.5 times faster than an Earth wind
> to get the same motive force. [The "mass" is the same but
> the force of Martian gravity only resists its motion 38% as
> much as Earth's gravity does. However, the inertia is the
> same on both planets, something to remember when you
> go for a walk on Mars.]
> The gravity may be less, but a Mars Walker would need
> to carry a lot of extra mass: solar panels for the cameras,
> radios, experiments, and other instruments, and weigh means
> more force and energy is needed. My guess is that a Mars
> Walker is a difficult and marginal thing. What I need now is
> a long term weather report on Martian wind speeds... from
> all over the planet.
>
>
> Sterling K. Webb
Received on Sat 14 Jul 2007 11:26:55 PM PDT