User Tools

Site Tools


wiki:link_for_instructors

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
wiki:link_for_instructors [2019/11/12 10:51]
ethanminot [Reflections from Fall 2019]
wiki:link_for_instructors [2019/12/15 12:34] (current)
ethanminot [Reflections from Fall 2019]
Line 9: Line 9:
 https://​physicstoday.scitation.org/​doi/​10.1063/​PT.3.4042 https://​physicstoday.scitation.org/​doi/​10.1063/​PT.3.4042
  
-Emilie du Chatelet (conservation of energy, pairs well with Emmy Noether):+Emilie du Chatelet (conservation of energy, pairs well with Emmy Noether)
 + 
 +In the final exam I notice reliance on a technique students have invented for themselves to circumvent physical reasoning. I've heard students call it "unit analysis"​. The basic ideaThe problem gives some numbers to solve the problem. Mash these numbers together in a way that gives the desired units. Here is a cautionary tale of how badly this approach can fail.  
 + 
 +**Estimate the lifetime of the Sun in unit of seconds:** First, piece together some facts about the Sun. The fusion of hydrogen atoms produces 1.3 x 10^12 kg.m²/s² of energy per atom. The surface area of the Sun is 4πR². The mass of the hydrogen fuel is 2 x 10^29 kg. Put these three quantities together and take the square root. Then I have something with dimensions of time (//t// = 2 x 10^30 seconds). Is this the lifetime of the Sun?
  
 ====== Reflections from Winter 2017 ====== ====== Reflections from Winter 2017 ======
wiki/link_for_instructors.txt · Last modified: 2019/12/15 12:34 by ethanminot