Screws

Consider a square threded screw-jack, which is used for raising a load W by applying a moment M to screw. If M is just sufficeint to turn the screw, the thread of the screw will slide around and up on the fixed thread of the frame. Consider the free-body diagram of the screw. The resultant reaction (normal reaction plus friction force) on one thread is represented by R , which is making an angle from the vertical. Note that .