On Wed, 20 Aug 2003 15:02:38 +0000 (UTC), guyscarsbrook{at}hotmail.com
(Guy Lux) wrote:

>I have often looked at the huge carnivore dinosaurs and wondered how
>they could have been mobile when so big.  There is some evidence to
>suggest that they were not such quick movers (something to do with the
>ratio of the femur/tibia length) but still, they are far larger than
>elephants who themselves are very slow, labored movers.
>
>I wondered if the lateral strike by the meteor that allegedly blacked
>out the sky, could have also had an effect on the earths
>gravitation. Could a lateral strike against the rotational direction
>of the earth have slowed down the rotation speed, reduced the
>centrifugal force, therefore increased gravity and as a consequence
>lead to the disappearance (or non-evolution following the mass
>extinction of the dinosaurs) of land creatures of massive prehistoric
>dimensions?
>
>
>Would be interested to know your thoughts.
>
>Guy

The effect of the earth's rotation on a body's weight is totally
insignificant.  It may be possibe to measure in a physics lab with
well calibrated instruments, but it has essentially no effect on
everyday life.

To be more specfic, the effect of gravity is measured by the
gravitational acceleration, g = 9.8 m/s^2.  The rotational
acceleration is w^2 r where w is the rotational velocity (one
revolution = 2 pi radians per day) and r is the radius of the earth
(approx 6400 km) The rotational acceleration turns out to be on the
order of 0.03 m/s^2 or 300 times smaller than gravitational
acceleration.  So if an animal were standing on the equator (the
rotational effect is less at higher latitudes) and the earth came to a
complete halt (which it didn't), the animal would increase in weight
by about 1/3 of one percent.  

Of course, there is absolutely no evidence that the rotation of the
earth changed significantly as a result of the asteroid impact.
Furthermore, any asteroid that could have such an effect would also
completely destroy the earth in the process.

We have machines that are as big as or bigger than the dinosaurs.
They are heavy and lumbering, but they can also reach rather high
speeds!





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Subject: Re: Gravity and dinosaurs
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Hi Guy,

Unfortunately I don't think that the gravity difference from the earth's
rotation is enough to account for the dinosaurs large size. I calculate that
the the Earth's rotation causes centrifugal acceleration at the equator
(where rotational velocity is 1674 km/h) and this effect means gravity is
only 5.186 microGal less at the equator than at the poles. See
http://www.dinox.freeserve.co.uk/english/gravnotes.htm for futher
information.

Various people have left comments on my web site about gravity changing due
to the earth's rotation which might interest you. Try typing "gravity
rotation" into the search section of
http://www.dinox.freeserve.co.uk/search.htm to see their comments.

I calculate that gravity at the time of the dinosaurs would need to be about
1/2 to 2/3rd the present value to account for their large size. An amazing
difference from the present! Perhaps even more amazing is that there is a
theory that predicts that the earth's gravity would be at this value during
the dinosaurs time - the expanding earth theory. This theory has been augued
about since the late 1950's and the debate is still rageing. See the geology
news groups for examples.

Regards,

Stephen Hurrell


"Guy Lux"  wrote in message
news:bi02ie$2fgl$1{at}darwin.ediacara.org...
> I have often looked at the huge carnivore dinosaurs and wondered how
> they could have been mobile when so big.  There is some evidence to
> suggest that they were not such quick movers (something to do with the
> ratio of the femur/tibia length) but still, they are far larger than
> elephants who themselves are very slow, labored movers.
>
> I wondered if the lateral strike by the meteor that allegedly blacked
> out the sky, could have also had an effect on the earths
> gravitation. Could a lateral strike against the rotational direction
> of the earth have slowed down the rotation speed, reduced the
> centrifugal force, therefore increased gravity and as a consequence
> lead to the disappearance (or non-evolution following the mass
> extinction of the dinosaurs) of land creatures of massive prehistoric
> dimensions?
>
>
> Would be interested to know your thoughts.
>
> Guy
>
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