College-Prep Physics: Which situation is more likely to rip the Levi’s jeans?
Today we did another round of voting to get at the idea that tension in springs, strings, and ropes are constant all the way through. Today’s slides:
During which, we do one of my favorite demos: What does the middle scale read?
In the end, we talk about how a seemingly unstretchable rope or spring actually stretches under tension, much like seemingly unbendable surfaces like tables deform under compression. Just like a solid can be modeled as a network of balls and springs, so can rope and string:
Even metal wire stretches!
NGSS Science and Engineering Practice #2: Developing Models
NGSS Science and Engineering Practice #6: Constructing Explanations
College-Prep Physics: I condensed a two-day sequence on tension (from Preconceptions in Mechanics) into one. The sequence gets at the nature of the tension force (it’s the same everywhere), the mechanism for tension (i.e., how do ropes “know” how hard to pull? It’s like a series of really stiff springs), and leads students to see that Levi Strauss’s famous logo
is physically equivalent to one in which one of the horses is replaced with a tree.
We ended with this demonstration of 3 springs scales connected in series by two ropes:
What does the middle scale read?
(Here’s the answer.)