How does a compound bow work, particularly the function of the cams and the “let off”?
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Disclaimer, I am not a archer or any expert in the world of bows, but I do have enough approximate physic knowledge to some what understand. aka, take my world with a bowl of salt.
The goal of a bow is to transform the energy of a archer INTO the kinetic energy of a arrow.
When you draw bow, you are essentially storing energy INTO the bent limbs.
When you release the bow, the limbs return to their neutral state, and such, release the energy into the arrow via the string, producing a forward thrust.
Surprise surprise, Energy imput to draw bow > energy of the arrow.
To make the arrow go fast, you store more energy into the draw, and we know energy = work X distance.
by using pully, we essentially extends the length of the rope, creating more distance, thus more energy stored.
As for let off, the Pulley system when combined, creates a non linear draw cycle, meaning, instead of gradually increasing the effort to draw as you extend a traditional bow, the compound bow peaks during your draw, and then falls off, thus at the maximum of your draw, you are actually using less effort to extend the bow compared to a traditional bow. This nonlinear makes perfect sense, because the total amount of work is conserved, its just the peak that was moved.
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