A heavier person descends faster than a lighter person

Just for not getting mixed in a political discussion, I thought of starting
a new thread :-)
Here my 2 cents:

A heavier person goes descends than a lighter person, because of the
potential energy.
This energy is build up during the climb, that's why heavier persons
generally aren't the fastest climbers as they need more energy to lift their
weight.

Formula for potential energy:

Ep = m * g * h;

E = Energy (in Joules)
m = Mass (in Kg)
g = Escapespeed of earth 9.81 m/s
h = Height (in Meter)

A person of 100 kg (bike included) needs 100 * 9.81 * 1000m = 981000 joules
to lift his weight 1000 m ( a serious pass) whereas a person of 70 kg (good
climber) needs 686700 joules.

This energy will be released, thus used to build up the speed on the way
down.
As long as the extra air resistance and mechanical resistance doesn't cover
the energy difference between the two, the heavier person will go faster.
I never saw the case that a heavier person went down slower than a tinyer
one.

When pedaling even more, the height will reduce faster and more energy will
be freed per second so that the speed increases even more. (Of course this
will depend on the slope too)

Koen De Poorter

I was suprised to find some RBR 'experts' not understand that a heavier
person would descend faster.
Just ride a light bike down a hill. Then ride a heavier bike down the
same hill. Makes a big difference. (Though of course the heavier bike
won't be as easy to turn with)

The potential energy isn't expressed as FASTER ACCELERATION. This is
fixed by the force of gravity. There are small aerodynamic differences
in small vs large people that have a small effect.

Basically the potential energy is expressed kenetically as a longer
roll out at the bottom of the descent.

Koen De Poorter wrote:

A heavier person goes descends than a lighter person, because of the
potential energy.

In reality, the rider and bike with the higher mass to drag ratio will
descend faster. If you had a heavier rider with a body shaped like a
parachute and a lighter rider shaped like a teardrop then the lighter
rider would go faster. This can be demonstrated simply by getting in
and out of an aero tuck while descending: same weight, different
speeds.

Mort

Right and I'd add the corollary that the heavier person descends faster
than he climbs!

On 10-11-2005 15:45, in article
, "Tom Kunich"
wrote:

The potential energy isn't expressed as FASTER ACCELERATION. This is
fixed by the force of gravity. There are small aerodynamic differences
in small vs large people that have a small effect.

When something falls with no obstruction, it accellerates with 9.81 m/s^2
This acceleration increases the kinetical energy.
When rolling down, kinetical energy is absorbed by friction.
(air+mechanical).

1 joule equals to 1 Newton meter. Energy is needed to accelerate.

See http://www.glenbrook.k12.il.us/gbssc...rgy/u5l1c.html

Basically the potential energy is expressed kenetically as a longer
roll out at the bottom of the descent.

Potential energy at the bottom = 0.

Koen

Ever heard of an Italian named Galileo? You might want to read some of
his work.

http://phyun5.ucr.edu/~wudka/Physics...ww/node49.html

http://www.iit.edu/~smart/martcar/lesson2/lesson2.htm

Koen De Poorter wrote:
Just for not getting mixed in a political discussion, I thought of starting
a new thread :-)
Here my 2 cents:

So if you feed a troll it will go downhill faster.

On 10-11-2005 16:53, in article
,
" wrote:

Ever heard of an Italian named Galileo? You might want to read some of
his work.

http://phyun5.ucr.edu/~wudka/Physics...ww/node49.html

http://www.iit.edu/~smart/martcar/lesson2/lesson2.htm


I don't see what you replying to anyway, those pages only describe
"freefalling bodies" hardly what a downhill rolling bicycle is. (Galileo
only calculates vertical movement, not the horizontal part which is rolling
speed)

I know that everything falls at the same acceleration and at the same speed
because of the gravitational force.

What's different is the energy something has. When you drop a 30 ton truck
from a hight of 10 meter it will release a lot more energy when hitting the
ground than that feather that theoretically falls at the same speed.

That energy (potential) is converted in kinetic energy (speed).
In a free fall (galileo's case) the potential energy is converted in kinetic
energy and is used to make the crater when it hits the floor (or converted
in warmth)

In the case of a downhill going bike the releasing potential energy is
converted in kinetic energy which in part drives your bike. (heavier persons
- more energy, going faster downhill)

That's enough explaining for me here.

Koen

Koen De Poorter wrote:
I don't see what you replying to anyway, those pages only describe
"freefalling bodies" hardly what a downhill rolling bicycle is. (Galileo
only calculates vertical movement, not the horizontal part which is rolling
speed)

I know that everything falls at the same acceleration and at the same speed
because of the gravitational force.

What's different is the energy something has. When you drop a 30 ton truck
from a hight of 10 meter it will release a lot more energy when hitting the
ground than that feather that theoretically falls at the same speed.

That energy (potential) is converted in kinetic energy (speed).
In a free fall (galileo's case) the potential energy is converted in kinetic
energy and is used to make the crater when it hits the floor (or converted
in warmth)

In the case of a downhill going bike the releasing potential energy is
converted in kinetic energy which in part drives your bike. (heavier persons
- more energy, going faster downhill)

That's enough explaining for me here.


Belgians, eh? They know cycling.

--
E. Dronkert