EOE-008 Cellphones in curved spacetime

Here we explore ideas for a cell-phone empirical observation exercise in the form of a "group outside-of-school lab experiment", inspired by these papers from McGill University [1-3] nearly a half century ago.

Setup: Imagine that there are two types of force, which can be used to describe motion not just in Newtonian "inertial frames" but also in accelerated frames and curved spacetime at any speed. Although the resulting motion will of course depend (at high speeds in a messy way) on the net force, these two individual force types are:

(i) Proper forces which are detectable by cell phone accelerometers, and include normal, rope, spring, friction and centripetal forces.

(ii) Geometric forces which are invisible to cell phone accelerometers, are associated with kinetic or potential energy differences connected to differential aging, and include gravity, inertial, centrifugal, Coriolis and tidal forces. These latter forces only arise in curved spacetimes and accelerated frames.

Assignment: Use a cell-phone accelerometer (e.g. with help from apps like Google's Science Journal and Vieyra's Physics Toolbox) or other methods [1-3] to measure some proper accelerations (magnitude and direction as a function of time) in your everyday world. These might include the upward "normal-force" acceleration experienced by a stationary object at the earth's surface, as well as accelerations of the metrolink, a braking car, an elevator, a carousel rider, the end of a simple pendulum, etc. Also if you get the chance, use a cell phone accelerometer or other methods to identify those accelerations (and/or the associated forces, energies, and differential-aging effects) which are geometric instead. 

Footnotes

• 1. P. C. Landry, F. M. Gurr, P. F. Hinrichsen, and R. B. Moore (1971) "The Acceleration of a Metro Train", The Physics Teacher 9, 441-446 link.

  2. Miriam S. Lafleur, P. F. Hinrichsen, P. C. Landry, and R. B. Moore (1972) "The Poisson Distribution", The Physics Teacher 10, 314-321 link.

  3. Mimi Lafleur and Fiona Gurr (1974) "Note: Physics Really does Work", The Physics Teacher 12, 235-237 link.