Silly as our application for this experiment may sound, we use this system to keep pens handy near the shopping list on the fridge. It’s saved us from many pen-searches over the years!
We install these at various places around the house (by the telephone, fridge, front door, anywhere that you usually need a pen at the last minute), and have even seen them at the counters of local video-rental stores.
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Download Student Worksheet
Troubleshooting: It’s important to note that the weight needs to slide freely both up and down the length of the cord (which is why fishing line is a great choice – the surface of the line is very low friction). Another important tip: the weights you use must weigh more than the object at the end of the string plus the force of friction in the lines (and the pulley). Hollow, metal objects work great like nuts (for bolts).
You’ll need to practice to find just the right balance point: where the pen flies up to its resting position when you let go of the pen.
This is a great addition to any tree house or playground structure! Hang a loop of rope from a tree branch (don't forget to thread the pulleys onto the rope before you tie the knot! Connect one pulley to the basket handle made from a circle of short rope. Tie a length of rope to the basket handle, then up through one tree pulley, down through the basket pulley, and up through the second tree pulley. Thread a 6" length of PVC pipe onto the end and tie the rope back onto itself to form a handle.
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