Re: California MSF Basic RiderCourse for an experienced rider ona liter bike?

 Odinn wrote:

Do you have a definition for 'center of gravity' ?  I understand the
definition of center of mass.  I don't know what 'center of gravity'
means.

The bike is a rigid body (excepting a very small amount of deflection
in the foam of the seat) for the purpose of evaluating this problem...
so other than the slight difference in center of mass (of the bike+
rider) caused by raising the rider's body an inch or so when taking
his weight off the seat cushion, the center of mass is essentially
unchanged despite the rider's weight being carried by the pegs rather
than the seat.

--
Mark  '01 SV650S  '86 GL1200A  '81 CM400T  '99 EX250-F13

 Mark Olson wrote:

The center of gravity is a geometric property of any object. The center
of gravity is the average location of the weight of an object.

Relocating the distribution of the weight from the seat to the pegs
lowers the COG.

http://www.grc.nasa.gov/WWW/K-12/airplane/cg.html

--
Odinn

"The greatest pleasure in life is doing what people say you cannot
do." --Walter Bagehot

Reeky's unofficial homepage ... http://www.reeky.org
'03 FLHTI ........... http://www.sloanclan.org/gallery/ElectraGlide
'97 VN1500D ......... http://www.sloanclan.org/gallery/VulcanClassic
Atlanta Biker Net ... http://www.atlantabiker.net
Vulcan Riders Assoc . http://www.vulcanriders.org

rot13 to reply

 Odinn wrote:

Here, I'll even do one better that deals specifically with motorcycles.
  A whole thread on it with it completely explained by none other than
Mark Ketchum (I hope I don't have to explain who he is).

http://www.ketchum.org/cgcm.shtml



--
Odinn

"The greatest pleasure in life is doing what people say you cannot
do." --Walter Bagehot

Reeky's unofficial homepage ... http://www.reeky.org
'03 FLHTI ........... http://www.sloanclan.org/gallery/ElectraGlide
'97 VN1500D ......... http://www.sloanclan.org/gallery/VulcanClassic
Atlanta Biker Net ... http://www.atlantabiker.net
Vulcan Riders Assoc . http://www.vulcanriders.org

rot13 to reply

 Odinn wrote:

N.B.  I am not claiming that putting your weight on the pegs has no effect
on the way the bike handles, simply that it does not change the center of
mass/gravity.

--
Mark  '01 SV650S  '86 GL1200A  '81 CM400T  '99 EX250-F13

 Odinn wrote:

To regurgitate a common phrase from Halliday and Resnick's _Physics_:

"What is really meant is mass, but historically the term weight was
in use"

The NASA website is accurately describing how to calculate the center  
of mass of an object, but they are using the term 'center of gravity'
instead of 'center of mass', presumably to conform to terms familiar to
a K-12 student.

I don't expect to convince you, but any 2nd year engineering student
should be able to understand, and hopefully actually calculate, (given
equations or finely divided volumetric data to describe the density
function and the shape of a bike and a human body) how the center of
mass of a bike and rider does not change simply by whether the rider is
supporting himself on the seat or the pegs, assuming he's only raising
his butt an inch or so off the seat.  Certainly putting your weight on
the pegs never *lowers* the center of mass or center of gravity, take
your pick, it *raises* it.  That's because in order to take the weight
off your butt, you have to push yourself off the seat slightly, which
raises your body's, and hence the combined bike+rider system's, center
of mass (or gravity, if you prefer).

--
Mark  '01 SV650S  '86 GL1200A  '81 CM400T  '99 EX250-F13