simple machines

Home

Chat

Blogs

Collection

Directory

Home : 2003 : March : 9

simple machines
By cherie

One of the most engaging ideas I've ever tried involved making a device whereby children could experience very directly the reduction in effort associated with pulleys. I cut a simple seat from a piece of 2x6 (about 15" long)
and drilled 1/2" holes in each of the four corners. I then made a trip to the hardware store and purchased about 25 feet of sturdy rope (like 1/2 inch polypropylene)and a several single pulleys (with hooks or holes to allow attaching them to your rope) that would work with that size rope.
Cut off 2 sections of rope about 6 feet long and thread one through each end of your seat,

bring the rope ends together above the seat, and securely knot them together (allowing enough room for a child to sit comfortably below the knot) Then attach a single pulley to the top of this. I then took the children outside to the pullup bars and presented a "rescue" scenario to them (e.g. someone larger than you has fallen down an embankment while on a hike)and proposed that using some rope and pulleys, they would be able to haul the person up. Then I went through a demonstration with a child volunteer sitting on the seat, adding pulleys to the system one at a time (fixed pulleys hanging from the bar above, moveable pulleys atttached to the load (the seat holding the child) until another child could easily lift the seat off the ground (for safety purposes, I only allowed them to raise the seat a foot or so). What they really thought was cool was when the effort had been sufficiently reduced that they could actually lift themselves. Then you can go back to the classroom and go through the math involved.
This cost me about $25, but was well worth it, plus it is very reuseable from year to year. Before you take it to your class the first time, try it out with an adult at a local park to make sure your knots and rope are secure, and to familiarize yourself with the best way to add pulleys to the system. Hope it works! My kids loved it.