Potential vs. Kinetic energy. We all learn this in school, but I had not actually used the terms together in 35 years. My son came home from school one day (eighth grade) with a project – build a marble track that demonstrated potential and kinetic energy.
Potential is when a ball is just sitting at the top of the hill – waiting to roll down as it were. Kinetic is when it starts moving and stays kinetic until it comes to rest. We want to show this. We also want to show how it looses energy over time (the three decreasing hills).
Requirements – it shall be minimum 2 meters long, it shall have one loop and it shall have 3 humps of decreasing size. If you are going to pursue a career as a business analyst or another roll where you gather requirements, be sure you learn the distinctions between ‘shall’, ‘will’ and ‘must’. Essentially, shall means ‘no exceptions’. Don’t do a ‘shall’, then you missed a requirement.
So we discussed how we should do it, the size (we needed to transport it to his class) and materials we might use. We looked around the garage at what was handy. Ton of wood! Hot glue gun with Super Strong glue (the most underrated tool for the creative type personality). Plenty to nails, screws, power tools, etc.
One of the lessons I wanted Liam to learn was that you can take things meant for one use and turn them around (metaphorically as well a technically) and use them in a different way from their intended purpose.
We lacked something to fulfill the ‘loop’ part of our requirements. So off to the hardware store and cruising the aisles. We came across some one inch thick tubing and bought five feet. Out tests at the store seemed to show it would work. We took a long PVC tube and dropped marbles into it and they (mostly) made it through. We bought PVC tubing as well that fit into the tubing.
Back home we started work on the base. The base was a piece of scrap plywood that we squared up on the table saw. We added a tall board to the end of our base, supported by a gusset.
Next we attached the coiled hose to the board and base. Sadly (and this was the most expensive thing we bought at about $10) it did not work consistently. And when it failed, the marble was stuck inside and you had to turn the whole unit upside down to get it out – not acceptable. The problem was the metal wire which, while helping keep the tubes shape, introduced friction and drag.
There were just enough small ridges to kill the marbles momentum. So, back to the drawing board.
I have a friend who had built a few of these and went to bum some parts from him
(this was also one of those, “Oh, uh, Dad, I’ve had this project several weeks but it is due in two days”, projects). While I thought the loop requirement was supposed to be closed, Liam felt it might not need to be so.
Terry had a piece of 6″ PVC tubing, about five inches long that was cut open, heated and pulled back.
This allows the marble to enter near the bottom, spin around and shoot out the top. While I was gone, Liam scrounged up some old red plastic bowls. Some serious hot glue gun work and you have a PacMan catching marbles. An exit hole was drilled into the bottom bowl.