Equus Pallidus asked my why a compound bow of a given draw weight shoots a faster arrow than a traditional bow of the same weight. The pulleys provide mechanical advantage making it easier to pull, but you should be losing energy due to friction, he says. And there is where you went wrong, EP.
A compound does lose energy due to friction in the wheels. But, the cables and pulleys on a compound bow aren't there to provide mechanical advantage. The pulleys are actually eccentric wheels. Picture a wheelbarrow with an oval shaped wheel. The resistance is hard, easy, hard, easy, hard, easy, when you push it. It is the same with a compound bow. The draw starts easy, hits a peak draw weight and then begins the let-off. Let off is a measure of the percentage of the draw weight at full draw compared to the peak weight. I have a 70 pound bow with 65% letoff. At full draw I only hold back 35% of the peak, or about 25 lbs. Equus Pallidus thinks that this is the great attraction to compound bows. You can hold the bow back for a longer time, due to the let off. It is a nice feature, but the main attraction is greater arrow speed.
The key to the greater speed of the compound is the draw force curve. Area under the curve is the energy stored by the bow. A compound is less efficient than a traditional bow. It just stores more energy, providing more energy to accelerate the arrow to a higher speed. A traditional bow typically uses wood arrows. I was told never to shoot wood arrows in a compound bow because it would blow them apart with the acceleration.
So what do you say EP?