Originally posted by fujimo:
lets say that a sample bow has excessively and unrealistically heavy tips. so the bow would be slower in accelerating those tips forward- but conversely would there not , theoretically be a greater shock when that forward momentum is halted by the string at the end of the stroke- assuming all other things are equal
i understand that the poor limb timing and poor design would lead to a greater vibration at the end of the stroke, but surely there has to be some kind of impact transferred to the limbs when that forward motion is halted- which would be greater where the kinetic energy is increased.
cos many many years ago when i went to school- the greater the mass of an object in motion- the greater the kinetic energy. and so when kinetic energy is abruptly halted it changes to potential energy- which in a bow- i would assume would be vibration in the limbs and down into the riser( Viz-hand shock).- so the higher the mass, the higher the kinetic energy- the greater the potential energy.
Pretty close!
The mass at the end of the limb doesn't really contribute to Potential Energy - the Potential Energy is that which is stored within the strained limb. Mass contributes to Potential Energy in the context of gravity and moving things through gradients.
But the more mass there is at the end of a limb, the more momentum that limb will have, so the more the limb resonates as the string closes the power stroke. Think of it like a pendulum - the longer it is and the more mass there is at the end of it, the more momentum it has. A bow transfers most of the energy into Kinetic Energy through the arrow, but the momentum of the limbs is dissipated throughout the bow as vibration. The more momentum the limbs have, the more vibration there is. The lighter the limbs are, the more energy is transferred into the arrow rather than dissipated throughout the limb. You can also think of it in the context of a tuning fork, which might be a better analogy.
The higher the weight of a bow, the faster the limbs travel, so the momentum is in turn increased. Therefore, more handshock for a given design.
Originally posted by fujimo:
i would think two limb tips exactly the same dimensions- one out of boo and one from osage- the difference in weight would be so negligible- so as not to make a noticeable difference???!??
Yeeeeeep. I think it was Tim Baker who said something along the lines of "Design trumps materials every time". I think the example he used was of a Red Oak Board Bow whooping the a*s off of a you-beaut Osage Stave Bow.
If you think about it, the denser a timber gets the stiffer it becomes (generally). So that means that, generally, the limb becomes thinner as density increases (and wider, dependent on tension/compression strength and assuming you are maintaining equal draw weight), offsetting the increase in mass at the limb tip.
I recently built a bow with heavy, static tips and thought it would be 'interesting'... Just about threw my shoulder out of joint! Anyway, went off track there a little but maybe it helped a little :rolleyes: I guess my point is, unless you're using wildly inappropriate materials, the effect they'll have on handshock is negligible compared to the design.
Topic: ? to the bowyers here (Read 1361 times)
