So... What the %$^! IS Virtual Mass???
01-08-2004, 04:40 PM
#11
Giant Nontypical
Join Date: Feb 2003
Location: Dover, PA USA
Posts: 5,497
RE: So... What the %$^! IS Virtual Mass???
Yeah sometimes I wish Ol' Norb could just follow up some of those reports with ........"Ok, for you dummies that means that this particular bow will be more efficient with heavy arrows"
I would be perfectly fine with the "you dummies" part. I qualify and would take no offense.
I would be perfectly fine with the "you dummies" part. I qualify and would take no offense.
01-09-2004, 06:41 AM
#12
Join Date: Feb 2003
Location: Chesapeake VA USA
Posts: 135
RE: So... What the %$^! IS Virtual Mass???
James Park wrote up a good explanation of virtual mass. Here it is:
"When you draw the bow you store energy. Not all of this energy gets to the arrow after the release, some of it is lost. A well established way of describing this is by the use of "Virtual Mass".
The way this works is that after release some of the stored energy of the bow is used to accelerate the arrow up to its final speed. The amount of energy that is lost could be described as being used to accelerate an effective mass of the moving parts of the bow (the "Virtual Mass").
So: the energy stored in the bow is split between the actual arrow mass and the bow's "Virtual Mass".
The arrow energy proportion is: (arrow mass)/(arrow mass + Virtual Mass).
The wasted energy proportion is: (Virtual Mass)/(arrow mass + Virtual Mass).
That is, the lower the arrow mass in proportion to the Virtual Mass, the lower the proportion of the bow's stored energy that ends up with the arrow. The lower the Virtual Mass, the more efficient the energy transfer will be, and the faster the bow.
The Virtual Mass is determined by many things: the mass of the string and other moving parts such as the limbs, cams and wheels, air resistance of the limbs, material losses in the limbs, etc.
You cannot measure the Virtual Mass directly. It is best measured by first measuring the fill percentage and the energy stored by the bow, and then measuring the velocity of an arrow of known mass. You can then calculate the Virtual Mass of the bow."
"When you draw the bow you store energy. Not all of this energy gets to the arrow after the release, some of it is lost. A well established way of describing this is by the use of "Virtual Mass".
The way this works is that after release some of the stored energy of the bow is used to accelerate the arrow up to its final speed. The amount of energy that is lost could be described as being used to accelerate an effective mass of the moving parts of the bow (the "Virtual Mass").
So: the energy stored in the bow is split between the actual arrow mass and the bow's "Virtual Mass".
The arrow energy proportion is: (arrow mass)/(arrow mass + Virtual Mass).
The wasted energy proportion is: (Virtual Mass)/(arrow mass + Virtual Mass).
That is, the lower the arrow mass in proportion to the Virtual Mass, the lower the proportion of the bow's stored energy that ends up with the arrow. The lower the Virtual Mass, the more efficient the energy transfer will be, and the faster the bow.
The Virtual Mass is determined by many things: the mass of the string and other moving parts such as the limbs, cams and wheels, air resistance of the limbs, material losses in the limbs, etc.
You cannot measure the Virtual Mass directly. It is best measured by first measuring the fill percentage and the energy stored by the bow, and then measuring the velocity of an arrow of known mass. You can then calculate the Virtual Mass of the bow."
01-09-2004, 07:29 AM
#13
Giant Nontypical
Thread Starter
Join Date: Feb 2003
Posts: 9,175
RE: So... What the %$^! IS Virtual Mass???
Okay... I was right there with the lesson all the way until it got to the part about 'fill percentage' and then suddenly I found myself outside in the blizzard of ignorance again. [
]
]
01-09-2004, 07:49 AM
#15
Boone & Crockett
Join Date: Feb 2003
Location: Lehigh County PA USA
Posts: 12,157
RE: So... What the %$^! IS Virtual Mass???
I was right there with you too Arthur. 
So, in other words, a bow that does not waste much energy into its limbs, cams, etc. in order to get them to work but instead transfers more energy into the arrow would then have a lower virtual mass figure and would then be more efficient....right?
As for measuring it indirectly...yeah, what is a "fill percentage"...in layman's terms?
Edited....
Robvos,
Ahhhh!
So, in other words, a bow that does not waste much energy into its limbs, cams, etc. in order to get them to work but instead transfers more energy into the arrow would then have a lower virtual mass figure and would then be more efficient....right?
As for measuring it indirectly...yeah, what is a "fill percentage"...in layman's terms?
Edited....
Robvos,
Ahhhh!
01-09-2004, 08:44 AM
#20
Boone & Crockett
Join Date: Feb 2003
Location: Lehigh County PA USA
Posts: 12,157
RE: So... What the %$^! IS Virtual Mass???
Who the %$^! really cares what it means.....It probably won't make you a better shooter than you already are......