Wednesday, August 13, 2014

Pulleys: How to Make a Simple Pulley

Recently, we started to learn about simple machines and lately have been focused on pulleys.  In particular, we wanted to explore what would make a good pulley so Jelly Bean, Jumping Bean and I explored the design features of a pulley.  Based on what we learned we were able to construct an effective pulley (that is also easy to make).


First we explored the pulley shape:  we used a simple wheel to see what would happen.   To make the pulley we thread a pipe cleaner through the wheel.  We hung the pulley (wheel and pipe cleaner) from a Command hook on the fireplace, and then we wrapped a piece of string over the wheel.


The string slid right off the wheel as Jumping Bean pulled on it.  Oops, this one didn't work.


We looked at another wheel that we could use and discussed how the two were different.  The girls first noticed that they were different color, but then realized that color would not make a difference in how the pulley would work.  They also noticed that one wheel was larger than the other and thought the larger one would work better.  After talking more about the differences, Jumping Bean noticed that one wheel had sides, or grooves, on it.  Jelly Bean quickly added that the "walls" would help the string from falling off.


We attached a weight (our ballet trophy) to one free end of the string and pulled on the other.   Nope, this one did not work either.  The sides, or grooves, were not deep enough to keep the string on the pulley.  So we looked at our supplies to see if we could find one with higher sides that might keep the string from sliding off.  The girls picked a cotton bobbin.


Victory!  The cotton bobbin had grooves deep enough to keep our string on the pulley allowing Jelly Bean to pull her trophy up to the mantle!


We then talked about how we could possibly make the pulley even more efficient.   By adding a washer on each side of the wheel we were able to reduce friction between the wheel and the pipe cleaner making it easier to pull.


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Supplies:
  • different types of wheels to test (cotton bobbin will work the best, it has deep grooves)
  • pipe cleaner
  • string
  • Command hook to attach to a ledge
  • washer- round plastic toy with a circle in the middle, real washer from tool box
  • toy
Instructions:
  1. Thread the pipe cleaner through the center of the wheel.
  2. Attach it to the command hook so the wheel is hanging over the ledge.
  3. Lay the string over the top of the wheel with the ends hanging down toward the ground.
  4. Tie a toy to the loose ends of the string and pull on the free end.
  5. Repeat with different types of wheels.
  6. Once you have determined which wheel works best, place a washer on each side of the wheel.
  7. Tie objects to the loose ends of the string and pull.  You have now made a pulley!
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