When does a rock stop being a rock?

When does a pebble stop being a pebble and become a stone?
When does a stone stop being a stone and become a rock?
When does a rock stop being a rock and become a boulder?

I ask my wife these three questions too frequently. She's had enough of my philosophizing. So maybe you can help me out here? Are the answers too subjective? Is there an objective, definitive, agreed upon set of answers to these questions? Are the answers determined by weight? size? volume? mass? density? ootsies? (a la Christopher Danielson)

I'm thinking bigger picture here: How do we bring this type of thinking or wondering to our students more often? When dealing with measurement, how do we get our kids to know the correct (or most logical) way to measure quantifiable items without telling them? Would asking these types of questions help encourage our students to be better problem solvers or be better at applying the right terminology?

So many questions... here's more:
Living in the USA, our customary units system of measurements seems counterproductive with inches, feet, yards, fathoms, miles, ounces, cups, pints, quarts, gallons, barrels, etc. Terminology can be difficult enough for students and to throw all these different measurements at kids (nay, humans) can only seem daunting. When should we use feet to measure something instead of inches or yards? I envy the metric system and, well, let's leave it at that. These measurement questions become even more relevant as I dive into estimation with my students and as I update estimation180.com each week.

I haven't posted in a while and feel like I need to ease back into my blogosophy (blogging philosophy?). I'm not sure I just eased back into it. What do you think here?

Rocky,
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Weekly Update Numero Uno

Hello everyone! It's time for the Solar Knights' weekly update for all of our dedicated fans and followers.

   We are making progress on Solar Knights 3. In the past week, Josh has touched up and fixed some of the wiring that was done on the car two years ago. At the same time, Matt has gone through every solar cell on the array and is busy making a detailed wiring diagram of it. Fernando has even looked into anything that could be fixed up on the bottom of the car!

Fernando checking the bottom of the car

Luis working on the motor controller's wiring

Our new recruits looking over our many documents on Google Docs

   Other important news, there is now a second solar car team in South Florida! Western High School has decided to join in the alternative energy challenge and build their own solar car.
   On Wednesday, the team payed the Solar Knights a visit to talk with us about how to properly build and wire a solar car. We started by showing them Solar Knight I & III then took them on a little journey to see Solar Knight II, which is resting peacefully in our team's trailer.
   Pictures of Western's visit are soon to come, so be on the look-out.

Be sure to come back next week to see our next weekly update and check on our progress! :)