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Re: Chain Hoist Operation



Here is a scan from Schaum's College Physics/ 8ed (minus the figure):

7.9 A differential pulley (chain hoist) is shown in Fig. 7-6. Two toothed
pulleys of radii r = 10 and R = 11 cm are fastened together and turn on
the same axle. A continuous chain passes over the smaller (10 cm) pulley,
then around the movable pulley at the bottom, and finally around the 11
cm pulley. The operator exerts a downward force F on the chain to lift the
load w. (a) Determine the IMA. (b) What is the efficiency of the machine
if an applied force of 50 N is required to lift a load of 700 N?

(a)Suppose that the force F moves down a distance sufficient to cause the
upper rigid system of pulleys to turn one revolution. Then the smaller
upper pulley unwinds a length of chain equal to its circumference, 2(PI)r,
while the larger upper pulley winds a length 2(PI)R. As a result, the
chain
supporting the lower pulley is shortened by a length 2(PI)R - 2(PI)r. The
load w is lifted half this distance, or (PI)(R - r) when the input force
moves a distance 2(PI)R. Therefore,
IMA=(distance moved by F)/(distance moved by w) =2R/(R-r)=22/1=22
(b)From the data,
AMA= (load lifted)/(input force) = 700N/50N = 14
and
Efficiency = AMA/IMA = 14/22= .64 = 64%


Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Tony Wayne" <wayne@PEN.K12.VA.US>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, June 20, 2003 10:54 AM
Subject: Chain Hoist Operation


| Can anyone describe how a manual chain hoist works? I've looked across
the
| internet and have only found products and demonstrations utilizing a
chain
| hoist.
| -Tony
| ==========================================================
| Tony Wayne Those that can, do.
| wayne@pen.k12.va.us Those that understand, teach.