Choke
Fig. 5
The second aspect is choke. This refers to the placement of your hand (or whatever is holding the object) on it. With a knife blade, it means how far up on the blade you hold (Fig 5). This makes an enormous difference in the rotation of the blade because of the counteracting force on the blade as it is released.
As the blade slides out of your hand and goes straight, your hand keeps traveling the arc. This means the blade is now moving out while your hand is still pushing on it. Normally, the blade would leave the arc and spin forward. With some choke, as the blade slides out and your hand is still following the arc, the pressure of your hand pushes the blade the opposite direction. This does not stop rotation, but will cause it to rotate at a different speed due to the momentum being put into it in the opposite direction. Choking up on the blade causes it to take longer to clear your hand, allowing more time for your hand to push as it travels the arc. This causes more energy to be transferred into the end as it leaves. Choking less means it will take less time to clear your hand and will, therefore, transfer less energy countering the rotation and rotate faster then if you choke more.
You may think the amount of choke would vary greatly depending on the length of the object. This is true. However, it can easily be thought of as a ratio according to the center point. If I take something, find an approximate center, then choke about three quarters of that from the end, it will throw roughly the same as a longer blade with a three quarter choke. “Roughly” is the keyword here. Remember the ice skater mentioned earlier? As the skater’s hands go in, the diameter shrinks and the speed increases. All the energy was spread out. When the skater’s arms move in, the same (or nearly the same, considering minor deceleration) energy is spread over a shorter distance causing increased spin. This just means you have to choke up a bit more on shorter knives then longer ones to get the same result.