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Old 12-09-2007, 06:48 PM   #9
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Originally Posted by JackSkellington View Post
lovely write up--I'm wondering, though, if ever to let the weight "freefall" even for only an inch or two. The correct method is to keep the weight in hand and move it back to horizontal without it ever leaving the hand? Since you say that putting a 1lb force on the top of the weight can translate to a 30 lb difference, I'm a bit curious because sometimes I'll press downward on the lever at the last string to compensate for slack, a bad habit I realize after reading this
Using my own dropweight machine as a "standard," I estimate that for each extra pound applied at the end of the tension bar, it corresponds to additional 15 pounds of tension imparted on the string.

Allowing the dropweight to drop a little bit shouldn't be too much of a problem. The elasticity of the string will pull back the dropweight, allowing everything to go back to the resting position. However, to drop it from a high position, the dropweight will pick up velocity as it drops down unimpeded at first, and it may create too great of a force and it can actually break the string.

Remember, Power = Force x Distance / Time.
If you allow the dropweight to drop too fast, it will create great power. It may be possible to break the string if you allow the dropweight to free fall from its highest position. No wonder big hitters break strings all the time.

Edited to add a better explanation: if you drop the dropweight from its highest point, it will pick up speed as it drops down. In other words, the dropweight is picking up kinetic energy. When the dropweight finally reaches its lowest point, the kinetic energy it has picked up will have to go somewhere: the string and the frame. If the strings cannot handle that energy, it will snap, and let's just hope your frame is still intact. That's why you need to allow the tension bar to drop slowly.
"Physics is like sex: sure, it may give some practical results, but that's not why we do it." -- Richard P. Feynman

Last edited by lethalfang; 12-09-2007 at 09:18 PM.
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