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The comparison between proper and geometric (classically called inertial) forces has a history which preceeds that of relativity because of the importance of accelerated frames in everyday life.
This is perhaps most simply illustrated [1] via the animation at right, where the red proper-force acting on our car driver appears to be accompanied by a geometric force (i.e. one which acts on every ounce of one's being and which vanishes locally with appropriate choice of a coordinate frame) from the driver's (car frame) point of view. General relativity has since told us quite generally that Newton's laws apply locally even in accelerated frames, provided that we consider geometric forces which arise from the "connection coefficients" associated with the coordinate system's metric.
Instead of going through existing resources one at a time here, we provide links below to example animations in this context, as well as places they might come in handy. Suggestions for other animations, as well as for "animation-restructuring" to make them useful for your applications, are invited e.g. on our traveler-kinematic discussion group linked at left.
Some relative motion animations for students to measure and analyze.
Some AP-physics empirical observation exercises developed therefrom.
References
P. Fraundorf (2016) "The proper-force 3-vector", HAL-01344268.
GIF animations, like the one at right and those linked below, allow students to make empirical measurements in space from individual animation frames (which contain residual images from previous frames) and in time with a stop watch. Subsequent analyses are predicated on data obtained separately by each student, thus giving them a taste of the full scientific observation cycle (...observe, model-selection, model-application, predict, design-future-tests...) rather than practice just plugging numbers into a given equation.
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