Simple Machines: Robert Graham Adriane Bennett • The Pulley
The pulley is essentially a variation of the axle and wheel; the wheel is grooved to guide a rope, chain or cable along the circumference of the wheel, which moves freely around the axle. At its most simple use, the pulley works to change the direction of force applied in a system. More complex uses of pulleys are frequently used to gain mechanical advantage in a system.
Types of Pulley System • Fixed (Class 1) Pulley • Moveable (Class II) Pulley • Combination (Class III) Pulley
Fixed (Class I) Pulley http://www.southeastclimbing.com/images/pulley1.gif
Fixed (Class I) Pulley • Often used to alter the direction of force in a system • Weight of force is equal to the weight of the object being moved. • Advantage is gained by moving the operator away from the load http://www.southeastclimbing.com/images/pulley2.gif
Floating (Class II) Pulley http://www.southeastclimbing.com/images/pulley2.gif
Floating (Class II) Pulley • Used to gain mechanical advantage to lift weight (W) by multiplying the forces • Weight of force (F) required to move the object is equal to the number of ropes (N) supporting the load (W). F = W/N http://www.southeastclimbing.com/images/pulley2.gif
Combination (Class III) Pulley http://en.wikipedia.org/wiki/Image:Pulley1a.svg
Combination (Class III) Pulley • Combines the Class I & II Pulleys in a more complex arrangement. • Often used to allow mechanical advantage in a system with operation in an alternate (offstage?) position.
Sample Project “Journey to the Heaviside Layer” NSU Production of “CATS” Fall 2007
Mathematical Computations P = W(sin[α]) P= Force of Pull Needed W= Weight of object being moved α = angle of incline
Mathematical Computations(all weights in pounds) P = W(sin[α]) P = (125 + 75)(sin) P = (200)(sin) P = (200)(.5) P = 100
Pulley Computations F = (1/n)(W) F = Force needed to move object n = number of Lengths of rope/cable in the system W= Weight of object being moved
Pulley Computations F = (1/n)(W) F = (1/2)(100 lb) F = 50 lb
References Oberg, Erik et al. Machinery's handbook : a reference book for the mechanical engineer, designer, manufacturing engineer, draftsman, toolmaker, and machinist. 7th ed. New York : McGraw-Hill, c1992. http://www.uark.edu/depts/aeedhp/agscience/simpmach.htm http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/incline.html http://www.southeastclimbing.com/faq/faq_pulley.htm (graphics) http://en.wikipedia.org/wiki/Pulley (graphics) CATS Production Team Production Directed by Barry B. Stoneking and Wm. Perry Morgan Costumes Design by Jessica Parr Scenic Design by Alan D. Ernstein Lighting Design and Production Management by Robert Graham Sound Design/Engineering by Shawn Parr Technical Direction by Philip Kidd Effect Operation by Charles Ruble, Mickie Marie, Kendall Judy Fabrication by Phil Kidd, Charles Ruble, Robert Graham, Ashley Crockett & L. Elizabeth Breitling