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===== Linear Acceleration: Instructor's Guide =====

==== Main Ideas ====

Accelerating reference frames cause simple motion to appear complicated.



==== Students' Task ====
//Estimated Time: 20 minutes, including wrap-up//

Students are asked to draw the trajectory of a ball thrown straight up on the station platform as
seen from a train accelerating through the station, for several values of the
(constant) acceleration.


==== Prerequisite Knowledge ====

Basic familiarity with Newtonian mechanics for constant acceleration.
Know the definition of trajectory (can be defined quickly).
Optional but helpful: motion diagrams (object is represented as a dot for equal time intervals)


==== Props/Equipment ====

  * [[:props:start#whiteboards|Small whiteboards]] with markers
  * [[http://www.physics.oregonstate.edu/~tevian/COURSES/ph429/2010/log/atrain.html|Pictures]] (transparencies or electronic) of several sample trajectories to show as solutions to students

==== Student Conversations ====

  * Some students draw motion diagrams, other draw trajectory graphs, but the students who draw motion diagrams seem to have a better understanding that the coordinate system is changing position in a time dependent way.
  * Some students don't recognize the parabolic shape is preserved (just rotated) - some students don't want to call this a parabola because it does not pass the vertical line test.

==== Activity: Wrap-up ====

  * First discuss the case of zero acceleration, but nonzero velocity, that the trajectory a parabola (the same as if the train is not moving but the ball has a non-zero horizontal component to the velocity).
  * Then slowly increase the acceleration (opposite to the velocity) (the parabola rotates so that the symmetry line is no longer vertical).
  * Is a boomerang trajectory possible? (Boomerang here means stops at the same location that it started - it actually looks like a line rather than a loop.)
  * Show prepared pictures/graphs if appropriate.

See [[http://www.physics.oregonstate.edu/~tevian/COURSES/ph429/2010/log/atrain.html|this page]] for further discussion.

==== Extensions ====

Which way does gravity (appear to) point on the train?