We like to begin an introductory physics course with a law of physics that applies to everything, has no known exceptions, and whose consequences are already familiar to students. That law is the principle of relativity. By focusing on the principle of relativity itself, and a careful selection of the thought experiments, we can comfortably introduce the basic concepts of special relativity that we will use later in the course.1 This allows us to construct an introductory physics course that includes 20th‐ and 21st‐century physics as we go along, rather than shoving modern physics off the back end.2
REFERENCES
1.
For an interesting discussion on the history of the principle of relativity as a physical law that applies to everything, see
Charles
Scribner
Jr., “Henri Poincaré and the principle of relativity
,” Am. J. Phys.
36
, 672
–678
(Sept. 1964
).2.
We have written two introductory physics textbooks, Physics2000 and Physics2000 Non‐Calculus, that begin with special relativity. Our main purpose was to explicitly demonstrate that such a course could include basic modern physics topics in a comfortably paced course, with no need for an extended edition. (The texts are discussed at www.physics2000.com.)
3.
Elisha
Huggins
, “Speed of wave pulses in Hooke's law media
,” Phys. Teach.
46
, 142
–146
(March 2008
).4.
In contrast, the well‐known formula for the speed of a transverse wave is , where the tension T equals the spring constant K times the length (L − L0) that the spring or Slinky has been stretched. Thus the speed of the transverse wave differs from that of a compressional wave by replacing the L by (L minus; L0) in Eq. (1), where L0 is the unstretched length. Since L0 is usually much smaller than L for a stretched Slinky, the compressional and transverse Slinky waves have about the same speed.
5.
David
Keeports
, “Demonstrating wave speed on a spring
,” Phys. Teach.
34
, 460
–461
(Oct. 1996
).6.
In the LC experiment, the resonant oscillation frequency f of an electric current moving between an inductor L and a capacitor C is . If L is a solenoid of length h, area AL, with N turns, and the capacitor C is a parallel plate capacitor of area AC and plate separation d, then using the formulas L = μ0N2AL and C = ε0AC/d, we can derive the result This result depends only on simple lab measurements that do not involve light.
7.
We have been asked if the numerical value of (μ0ε0) could change due to the motion of the observer. If the principle of relativity is correct, the answer is no. Imagine a spaceship passing by us on the way to colonize a planet. Suppose students in that spaceship did the LC experiment and got a different value for . Reading Earth‐based physics texts, the students could conclude that the change in the value of (μ0ε0) was due to the uniform motion of the spacecraft, and thus the LC experiment could be used to violate the principle of relativity.
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© 2011 American Association of Physics Teachers.
2011
American Association of Physics Teachers
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