Wednesday, August 6, 2014

Exploring How Pulleys Reduce Friction

We recently started playing with pulleys and they are so much fun!!  As an adult this is my first time really playing with pulleys (all previous exposure has been theoretical) and I might be enjoying it more than the kids.

To start exploring pulleys we introduced how pulleys reduce friction.  I like this as an initial activity as friction is a topic we have visited a few times before {here and here}.  The other thing that I like about this activity is that it takes two kids working together and I always like it when the girls can learn to do something by helping each other (especially when little Bear can participate too).

First we took a long piece of yarn and threw it over the door.  Then each girl stood on the opposite side of the door and alternated pulling on the yarn.

We counted how many pulls until the yarn broke - it took the girls about 25 pulls (in comparison it took me doing it by myself about 3).  The girls battled a bit with keeping the yarn tight to ensure good friction when it was their turn to release in the back and forth.  So we worked on pulling harder and keeping it tight.  Unfortunately this meant that Bug (bigger) pulled really hard which pulled the yarn out of little Bears hands and gave her a mild rope burn.  So little Bear did not want to help much after that.  I would recommend tying something like a rod on the smaller child's side to give them a better grip and to reduce the chance of rope burn if one child does pull too hard.

We spoke about how the top of the door was rough and so there was a lot of friction on the yarn when we pulled which made lots of little cuts - like a bread knife going through a loaf of bread.  So what would happen if we make something with less friction?  To do this we made a simple pulley from a cotton bobbin and a pipe cleaner and hooked it over the door.   We closed the door to keep the pipe cleaner up.  If you find just the right spot on a cupboard door it will hold really well (as long as the kids don't yank).

The girls alternated pulling again to see if we could get to a higher number of pulls.

YAY!  We went on for a while!!  The pulley reduced the friction on the yarn when pulling.  The pulley did come off the door once when we did a really big pull but it held for normal pulls.  You may need some reinforcement if you have a child who is really excited.


  • yarn - about 8 feet long
  • door
  • cotton bobbin
  • pipe cleaner


  1. Lay the yarn over the door.
  2. Have a child hold each side and alternate pulling down.  Count how many pulls until the yarn breaks.
  3. Make a pulley by putting a pipe cleaner through a cotton bobbin.  Hook the ends of the pipe cleaner over the door and close the door to secure the attachment.
  4. Loop the yarn through the pulley.
  5. Repeat the alternating pulling on the string to see if you can get to a higher number of pulls


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