Poe, Poe, Pitiful me

10 physics misconceptions, explained poorly

[This blog post was written by a guest columnist, a D-student in freshman physics who will remain anonymous]

It’s pretty obvious it’s not, even accounting for Poe’s law (as applied in this case, one could not tell the difference between a D- student and a professor pretending to be a D- student, were the professor able to avoid succumbing to snark. Or hyping his book.). The misconceptions are very real, though. One of my favorites, much more plausibly true, is the one about heavy boots.

In my teaching days I saw plenty of these. So much so that we once played a game of “GCE Jeopardy!” at a party my housemates and I threw. The answer was given, and one had to name the Gross Conceptual Error (GCE) that would have elicited the response. For example, if the answer in the “mechanics” topic was “It is always conserved”, the proper GCE question would not be energy, since that’s actually conserved. It would be “what is momentum?” Some students would invariably insist that momentum was always conserved, even in the cases where a net force was acting. Which counts as a gross conceptual error.

5 thoughts on “Poe, Poe, Pitiful me

  1. Momentum is as always conserved as energy. Energy is only “always conserved” if you expand your concept of “the system” to include all things interacting. Momentum is “always conserved” under the exact same considerations.

  2. As a high school physics student, it was more useful to think momentum is always conserved (in collision problems, say) than it was to think energy was, because occasionally the collisions were inelastic. You could rely on momentum in a collision problem but not always energy.

  3. And why beholdest thou the mote that is in thy brother’s eye, but considerest not the beam that is in thine own eye?” These people have physics PhDs (and presumably perambulate barefoot),

    arXiv: 1304.0038, 1201.4147, 1201.1368, 1201.1322, 1112.2689, 1112.1299, 1112.1222, 1112.0815, 1112.0527, 1112.0353, 1112.0300, 1111.7268, 1111.7181, 1111.7050, 1111.6579, 1111.6330, 1111.6330, 1111.4931, 1111.4532, 1111.3888, 1111.2271, 1111.1574, 1110.6697, 1110.6673, 1110.6577, 1110.6571, 1110.6408, 1111.0805, 1111.0733, 1111.0502, 1111.0286, 1111.0093, 1110.4754, 1110.3763, 1110.3540, 1110.3581, 1110.3266, 1110.3071, 1110.2463, 1110.2236, 1110.2219, 1110.2170, 1110.2146, 1110.2060, 1110.2015, 1110.1943, 1110.1875, 1110.1790, 1110.1330, 1110.1253, 1110.0969, 1110.0931, 1110.0889, 1110.0813, 1110.0762, 1110.0755, 1110.0697, 1110.0644, 1110.0456, 1110.0451, 1110.0449, 1110.0245, 1110.0239, 1110.0234, 1109.6930, 1109.6667, 1109.6631, 1109.6624, 1109.6354, 1109.6312, 1109.6296, 1109.6282, 1109.6170, 1109.6160, 1109.6121, 1109.6055, 1109.6005, 1109.5721, 1109.5671, 1109.5651, 1109.5357, 1109.5172

    It was a loose fiberoptic connector in the timing circuit.

  4. @BlackGriffen That’s a concept that physics 101 students don’t usually grasp and is also typically not helpful in solving problems.

    @Cap’n I’m sure that’s one source of the confusion.

  5. One possibility–which seems in principle testable–is influence from movies. We see folk let go of stuff in sci-fi and they float away. Rarely does this happen to people in the movies. I.e. people dont usually float in the the films to indicate “spacey”. 2001, Firefly, Sunshine and Gravity are honourable exceptions to the rules of movie physics.
    Its tough to find populations who have not seen sci fi these days but maybe its possible?

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