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The screw Simple machines in technical theatre

Delbert Hall and Stew Ives. The screw Simple machines in technical theatre. Introduction. The screw is a modified version of the inclined plane.

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The screw Simple machines in technical theatre

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  1. Delbert Hall and Stew Ives The screwSimple machines in technical theatre

  2. Introduction • The screw is a modified version of the inclined plane. • While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp similar to that of a spiral staircase.

  3. Calculating Pitch • The distance between two adjacent screw threads is called the pitch of a screw. • For example, if you place a ruler parallel to a screw and count 10 threads in a distance of one inch, then the pitch of the screw would be 1/10.

  4. The Mechanical Advantage of the Screw • The screw is often turned by another simple machine such as a lever or a wheel and axle. • In this case, the total mechanical advantage is equal to the circumference of the simple machine to which the effort force is applied divided by the pitch of the screw. • This is sometimes referred to as the “Idea Mechanical Advantage” because is does not take into account any friction.

  5. Converting Linear Motion • Turning the screw one complete revolution will move it into or out of an object a distance to the pitch of the screw, or .1” in this case. Therefore, a screw can be used to convert circular motion into linear motion • 1 Revolution’s Distance = Pitch of Screw

  6. Mechanical Advantage • The formula for determining the ideal mechanical advantage of a screw is: IMA= 2pL/P • Where L = length of the lever and P = 1 pitch

  7. Comparison of Mechanical Advantage:

  8. Achieving Mechanical Advantage • The ideal mechanical advantage is of little meaning since there is typically a lot of friction.* • However, the screw is an enormously useful in when pressure is needed to seal the lid onto a jar, a top on a bottle, hold a light bulb in its socket or hold two pieces of wood or metal together. • *(Note: Ball screws are used in some machines to greatly reduce friction.)

  9. Other Uses • Because of the mechanical advantage of a screw, it is also useful for moving heavy loads. Such screw driven devices include garage door openers and jacks.

  10. How else can we use the Screw in Theatre? • We can use the same concept behind an adjustable piano bench to lift a platform.

  11. Raising a Platform with the Screw • Applying force to the lever rotates the long Screw • Using a longer lever increases our Mechanical Advantage • This Expands the Scissor Jacks and makes the Platform Rise

  12. References: • http://www.cosi.org/files/Flash/simpMach/sm1.html • http://www.uark.edu/depts/aeedhp/agscience/simpmach.htm • http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/incline.html

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