摘要:

Many relativistic formulas can be derived without explicitly using Lorentz transformations but, instead, directly from Einstein’s postulate: ‘‘All physical laws are the same for all inertial observers.’’ These formulas include time dilation, addition of velocities, the Doppler effect, and optical aberration. From the visual picture seen by one observer, one can deduce the picture seen at the same space‐time point by any other observer, without knowing anything about the speed or the three‐dimensional shape of the observed object. In particular, the apparent visual shape of a moving object is not contracted, but rotated.

ISSN:0002-9505    

DOI:10.1119/1.15106

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

This article presents a numerical alternative for treating the propagation of uncertainty in a function that depends on random experimental variables. With the help of microcomputers, this technique can be used by students at all levels in a college physics curriculum and is particularly useful when there are a large number of such calculations to do or the function involved is complicated due to the number of variables present or the explicit functional form. The numerical procedure can even be used with a function that cannot be expressed analytically, but is given instead in the form of a table or graph. Finally, the technique does not require knowledge of partial differentiation or multivariable Taylor series expansions in contrast to the traditional treatment of the propagation of uncertainty.

ISSN:0002-9505    

DOI:10.1119/1.15107

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

Einstein’s treatment of stimulated emission, spontaneous emission, and absorption yields the Planck distribution law for photons if the ‘‘atoms’’ with which the photons interact are described by the Boltzmann distribution. We show that the Planck law is also obtained when the photons interact with matter that is described by either Fermi–Dirac or Bose–Einstein distributions.

ISSN:0002-9505    

DOI:10.1119/1.15108

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

Many common observations are inexplicable by single‐scattering arguments: the variation of brightness and color of the clear sky; the brightness of clouds; the whiteness of a glass of milk; the appearance of distant objects; the blueness of light transmitted in snow and other natural ice bodies; the darkening of sand upon wetting. Yet multiple scattering is seldom mentioned in optics textbooks. It is possible to understand many observable phenomena without invoking the complete theory of multiple (incoherent) scattering. A simple two‐stream theory, in which photons are constrained to be scattered in only two directions, forward and backward, is adequate for interpreting many observations, even quantitatively, and it paves the way for advanced study.

ISSN:0002-9505    

DOI:10.1119/1.15109

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

The history of science has known for quite some time that Newton’s very first concept of centripetal force is derived from a simple model of a particle bouncing elastically in a polygonal path from a circular constraint. Fully described by Isaac Newton himself in his ‘‘Principia’’ 300 years ago, the model does not seem to have caused any response in physics courses or textbooks.

ISSN:0002-9505    

DOI:10.1119/1.15110

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

Rigid body dynamics are used to describe the motion of parachute‐payload systems released from aircraft. Two models are developed to describe the transitional and rotational degrees of freedom using the dynamical equations of Newton and Lagrange. The latter mechanics treats the parachute and payload as two rigid bodies in contact, while the former mechanics treats the entire system as a single rigid body. Finally, the equations of motion deduced from the Newtonian approach are numerically solved for a stabilization parachute to show the effects of wind and of suspension line length on damping.

ISSN:0002-9505    

DOI:10.1119/1.15111

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

A system of ten computers has been used for 2 yr in a general physics laboratory. This article lists the experiments in which standard laboratory equipment is replaced by on‐line use of the computers. The durability of the computers and student reaction to the system are evaluated. In addition, hardware, software, and books found helpful in setting up and running the system are described.

ISSN:0002-9505    

DOI:10.1119/1.15112

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

The mathematics describing the appearance of the ground trajectories of geosynchronous satellites is given in terms of vector geometry and orbital mechanics in a form familiar to physics students. The dependence of the trajectories on orbit inclination, eccentricity, and location of perigee is shown. The formalism is also seen to apply to the description of the analemma and to permit prediction of the appearance of the analemma in future epochs.

ISSN:0002-9505    

DOI:10.1119/1.15113

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

The Schrödinger equation for a spin‐ 1/2 neutral particle with a magnetic dipole moment interacting with a helical periodic magnetic field of arbitrary strength and period is solved exactly. The solution is easily obtained by exploiting the symmetries of the Hamiltonian and it is expressed in terms of elementary functions. Several interesting physical aspects of the solution emerge. The behavior of the spin, the group velocity, and the effective mass tensor are obtained, yielding some novel and nontrivial results. Because of the mathematical simplicity, this problem is particularly suitable for an elementary graduate course in quantum mechanics.

ISSN:0002-9505    

DOI:10.1119/1.15114

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP

摘要:

The similarities and differences between diffraction from single slits and scattering from single fibers can be dramatically demonstrated by some simple experiments. Geometrical properties such as fiber size, cross section, tilt, and nonuniformity all contribute to the intricate detail of the diffraction pattern. An examination of the role of the complex refractive index, polarized light, and geometrical effects in scattering phenomena will contribute to a deeper understanding of the interaction of light with small apertures and particles.

ISSN:0002-9505    

DOI:10.1119/1.15115

出版商:American Association of Physics Teachers    

年代:1987

数据来源: AIP