30 Jan 2004 05:12:43
GR
heavy downhill faster???

Previous discussion cited several instances of heavier folks going downhill
faster (bikes and skis) than lighter folks.
Several people seemed to agree that the physics works this way.
Am I missing something major? Didn't Galileo drop large and small
cannonballs and have them hit the ground at the same time (showing that
weight doesn't make a difference)?
http://www.spartechsoftware.com/reeko/Experiments/gravity.htm for a little
info.
gr




30 Jan 2004 07:03:13
david emile lamy
Re: heavy downhill faster???

"GR" <greif1@nospamrochester.rr.com > writes:

> Previous discussion cited several instances of heavier folks going downhill
> faster (bikes and skis) than lighter folks.
> Several people seemed to agree that the physics works this way.
> Am I missing something major? Didn't Galileo drop large and small
> cannonballs and have them hit the ground at the same time (showing that
> weight doesn't make a difference)?
> http://www.spartechsoftware.com/reeko/Experiments/gravity.htm for a little
> info.
> gr

Acceleration due to gravity is independent of mass in a vacuum.

What you are missing is fluid resistance. In cycling once you crest 20mph then
air resistance consumes at least 80% of your energy expenditure. That is why
drafting is such an effective stategy for cyclists. For that matter, drafting
a good pair of feet is the best way to survive the triathlon swim. Air is a
fluid like water.

So when the speed of travel through a fluid increases, then fluid resistance is
proportional to the cube of velocity. Since more massive human bodies tend to
have a smaller proportional frontal area to those with a mass deficiency, then
for a brief shinning moment the heavier cyclist (or skier) descends more
rapidly.

But hauling it (your carcass) up an incline is what wins any cross-country race
whether on skis, wheels or running shoes and the less massive usually have the
superior strength to weight ratios and hence are better ascenders.

--
gnupg fingerprint: 06AE 6472 EEE3 60B5 764D 110F F09F 74D8 B389 22F8


30 Jan 2004 23:17:15
Aliant
Re: heavy downhill faster???

Yes, he did, and an Apollo crew dropped a feather and a hammer on the moon.
(http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html)

But if Galileo had Swiss timing available, he may have noticed a slight
difference in the time, due to the drag caused by the difference in surface
area of the two cannon balls. As if fluid dynamics were not enough, the
skier has to contend with the effect of static and dynamic friction on the
ski / snow interface, which is affected by the mass (weight) of the skier.

-S.

"GR" <greif1@nospamrochester.rr.com > wrote in message
news:fJlSb.8095$%72.3652@twister.nyroc.rr.com...
> Previous discussion cited several instances of heavier folks going
downhill
> faster (bikes and skis) than lighter folks.
> Several people seemed to agree that the physics works this way.
> Am I missing something major? Didn't Galileo drop large and small
> cannonballs and have them hit the ground at the same time (showing that
> weight doesn't make a difference)?
> http://www.spartechsoftware.com/reeko/Experiments/gravity.htm for a
little
> info.
> gr
>
>