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A thread on pseudo-forces in classical mechanics inspired by a discussion on @WKCosmo 's wall. Students should know what a pseudo-force is. Unfortunately many text books over-emphasize the use of it to the extend it leads to a *wrong* understanding by students. How? 1/7
It is seldomly so that a non-inertial frame is more handy for computations and, more importantly, obscures what really happens. Consider the tower of Pisa experiment. Text books typically set up an approximation to arrive at the distance the ball traveled to the east. 2/7
The computation is lengthy and only an approximation. Whereas in the inertial frame it is simply the problem of an object falling to the earth with an initial velocity to the east. Not more. Students get so lost in the technical computations they forget this simple fact. 3/7
Other example: students that learn about pseudo-forces get lost in differential equations when you ask them how much a rocket would miss its target when it is launched at the North Pole and aimed at say, Brussels. Whereas it is trivially just the earth rotating underneath. 4/7
The best illustration is when I ask students to compute "the tower of Pisa" trajectory for people living on the inside of circular spaceships (in outer space) whose rotation mimics earths gravity to some extend. High school students do better than university students here. 5/7
Why? High school students typically do not know pseudo-forces and realize the ball is following a straight line in outer space (problem is trivial). University students unleash non-inertial frames and get a differential equation they typically cannot solve. 6/7
This phenomenon of understanding less by knowing more should be called "negative knowledge". 7/7
