Tech Support: Ropes and Pulleys



Helpful Tips

  • You must place CPO weights on the bottom block before you can operate the pulley system properly. All experiments call for 4 square washers to be placed on the bottom block.
  • When students measure the amount of string they pull to raise the bottom block to a certain height off the table, show them how to use the black cord stops as markers. Simply slide both cord stops down the string so they rest against the top block. When you operate the pulley, pull the string by holding on to the cord stops. When you have raised the bottom block the required distance, slide one cord stop back so that it once again rests against the top block, and measure the distance that now exists between the two cord stops. This will be equal to the distance that you pulled the string to raise the bottom block.
  • To prevent the block and tackle system from tipping over, have students pull the string directly down toward the table, rather than out to the side. Pulling the string out to the side can make the whole system unstable.
  • When measuring distance traveled by the lower pulley block, use the holes in the physics stand as references. They are exactly 5 cm apart.


Q: Why is the yellow pulley string (tackle) so long? It's very awkward for my students!

A: You need a very long piece of string to rig up all 6 pulleys.

Q: What are the black cord stops for?

A: These come in handy when students are determining the length of string that they pulled to raise the bottom block a certain height. See tip #2.

Q: Why is there an eye hook on both the top and bottom blocks?

A: This is so you can switch the brass clip from bottom to top, rig up all possible pulley combinations, and always pull the string down toward the table. If you only attach the string to the top block, you will have to pull up on the string to operate the pulley for some combinations.

Q: What is the red string for?

A: The red string is known as the "safety string". This keeps the top and bottom blocks "attached" to one another, so if the yellow string slips off during use, the bottom block will not fall off the entire assembly.