摘要:

The coefficient of restitution of major league baseballs is required to be 0.546±0.032. These allowed variations affect the launch velocity and ultimately the range of fly balls. The variations in the range for well‐hit balls are calculated here to be on the order of 15 ft. These calculations provide an interesting collection of mechanics problems that might be of interest for undergraduate students.

ISSN:0002-9505    

DOI:10.1119/1.16224

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

By making use of the Stokes operator and its corresponding dual operator, which are introduced here, a short proof of the Helmholtz theorem for antisymmetric second‐rank tensor fields in Minkowski space‐time is presented.

ISSN:0002-9505    

DOI:10.1119/1.16225

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

It is argued that the age of the universe may well be numerically finite (20 billion years or so)andconceptually infinite. A new and natural time scale is defined on a physical basis using group‐theoretical arguments. An additive notion of time is obtained according to which the age of the universe is indeed infinite. In other words, never did the Big Bang begin. This new time scale is not supposed to replace the ordinary cosmic time scale, but to supplement it (in the same way as rapidity has taken a place by the side of velocity in Einsteinian relativity). The question is discussed within the framework of conventional (big‐bang) and classical (nonquantum) cosmology, but could easily be extended to more elaborate views, as the purpose is not so much to modify present theories as to reach a deeper understanding of their meaning.

ISSN:0002-9505    

DOI:10.1119/1.16226

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A simple mechanical system formed by two bodies joined by means of a rigid bar and constrained to move in orthogonal directions is presented. The behavior is analogous to that of a special type of simple harmonic oscillator: The frequency depends on the initial conditions whereas the amplitude always turns out to be the same.

ISSN:0002-9505    

DOI:10.1119/1.16227

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

This article presents a calculation of the error in parameters derived from the least‐squares method of fitting nonlinear models to experimental data. The formula reduces to the well‐known result for the case of a linear least‐squares fit. It differs, however, from a method for calculating the error that is often employed for the nonlinear case. The difference between the current result and that method’s is illustrated with examples from least‐squares fits to spectroscopic data.

ISSN:0002-9505    

DOI:10.1119/1.16228

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The intuitive concept of homogeneity is developed into a physical quantity to provide a qualitative level of description for thermodynamic systems. The treatment gives some insight into the relation of entropy, disorder, and homogeneity.

ISSN:0002-9505    

DOI:10.1119/1.16229

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

A simple semianalytical calculation is used to study how a star reacts when its central stock of hydrogen is exhausted and before the next fusion reaction based on helium begins.

ISSN:0002-9505    

DOI:10.1119/1.16230

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

An explanation is provided of the differences between the mksa and esu systems used in the study of nonlinearities in the optical properties of materials used in optical waveguides. Means of converting both units and quantities between the two are presented, and the relationship between the electric susceptibility tensors defined in the two systems is demonstrated.

ISSN:0002-9505    

DOI:10.1119/1.16231

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

摘要:

The impulse delivered to the end of an electromagnetic transmission line is calculated explicitly, using techniques of university sophomore‐level physics and calculus. The result is obtained for the open‐circuit end, the shorted end, and for arbitrary resistive termination, and without solving for the fringing electric field or the current density distribution in the terminating resistor. Equating impulse to momentum transfer yields the relationshipE=pcfor electromagnetic propagation of energy.

ISSN:0002-9505    

DOI:10.1119/1.16180

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.16181

出版商:American Association of Physics Teachers    

年代:1990

数据来源: AIP