The classic film “Frames of Reference”1,2 effectively illustrates concepts involved with inertial and non-inertial reference frames. In it, Donald G. Ivey and Patterson Hume use the cameras perspective to allow the viewer to see motion in reference frames translating with a constant velocity, translating while accelerating, and rotating—all with respect to the Earth frame. The film is a classic for good reason, but today it does have a couple of drawbacks: 1) The film by nature only accommodates passive learning. It does not give students the opportunity to try any of the experiments themselves. 2) The dated style of the 50-year-old film can distract students from the physics content. I present here a simple setup that can recreate many of the movies demonstrations in the classroom. The demonstrations can be used to supplement the movie or in its place, if desired. All of the materials except perhaps the inexpensive web camera should likely be available already in most teaching laboratories. Unlike previously described activities, these experiments do not require travel to another location3 or an involved setup.4,5

1.
Physical Science Study Committee
, “
Frames of Reference
” (
Educational Services
,
1960
). Available on DVD from AAPT at aapt.org/Store.
2.
For a transcript of the film with additional discussion of motion in a rotating frame, see
A.
Steyn-Ross
and
D. G.
Ivey
, “
‘Frames of Reference’ revisited
,”
Am. J. Phys.
60
,
1069
1085
(
Dec. 1992
).
3.
R. W.
Robinett
, “
It's, like, relative motion at the mall
,”
Phys. Teach.
41
,
140
142
(
March 2003
).
4.
L. T.
Escalada
,
R.
Grabhorn
, and
D. A.
Zollman
, “
Applications of interactive digital video in a physics classroom
,”
J. Educ. Mutinied. Hypermedia
5
,
73
97
(
1996
).
5.
R. B.
Sawyer
, “
Projectile motion in different frames of reference
,”
Phys. Teach.
6
,
178
(
April 1968
).
6.
For example, the excellent Tracker software created by
Douglas
Brown
, available for free at www.cabrillo.edu/∼dbrown/tracker/.
7.

When a student points out that the tray had to accelerate initially before continuing to move at constant velocity, take the opportunity to discuss the role static friction plays during that time.

8.

In this case, a normal force from the groove in the ramp compensates for the inertial force during the initial acceleration of the tray.

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