摘要:

A method is described whereby, using primitive equipment, anyone can measure the size of the Earth, to an accuracy of order of magnitude 10% — by observing two sunsets in the space of a few seconds. The calculated result’s closeness to the truth is comparable to the best extant ancient estimates.

ISSN:0002-9505    

DOI:10.1119/1.11880

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

A system consisting of two point charges has an energy contribution from the system electrostatic potential energy and accordingly a contribution to the system mass given by this energy divided byc2. Here we investigate the change in weight associated with the electrostatic potential energy for a system of two point charges supported side by side against a weak gravitational field. The gravitational distortion of the Coulomb field of a point charge is calculated using the equivalence principle, and it is then shown that the change in the two‐particle system weight can be understood precisely as the change in supporting force necessary to balance the electric force of each charge upon the other. The example provides a clear illustration and detailed mechanism for understanding the mass‐energy connection for weak gravitational fields.

ISSN:0002-9505    

DOI:10.1119/1.11881

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

An apparatus is described which allows one to study the speed distribution, the gravitational distribution, and the mean free path of steel balls agitated into two‐dimensional motion through collisions with the moving walls of their enclosure.

ISSN:0002-9505    

DOI:10.1119/1.11882

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

It appears, from the recently published ’’illustrative test’’ and the sample questions which were published previously and from the list of topics, that the new Medical College Admission Test contains a large number of physics related questions in the chemistry section in addition to those in the physics section. Also, many of the questions in the reading and quantitative analysis skill section are of concern to physics teachers who hope their students learn to read carefully and to analyze data. Although most questions are straightforward at a reasonable first year level, there are a disturbing number of questions that seem ambiguous. Physics teachers should be concerned about such shortcomings of a test that plays a major role in the career of many of their students.

ISSN:0002-9505    

DOI:10.1119/1.11883

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

The power of symmetry and simple geometrical arguments is demonstrated in this somewhat unusual treatment of projectile motion. Keeping calculus and trigonometry manipulations to a bare minimum, the motion is analyzed in its greatest generality. Direction of velocity at any point, range, time of flight, maximum height, safety parabola, and maximum range are deduced for a projectile launched upon a plane inclined at any angle with respect to the horizontal.

ISSN:0002-9505    

DOI:10.1119/1.11884

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

It is an enigma for students why artists use red, yellow, and blue as primary colors, whereas physicists use red, green, and blue. To answer this problem, the spectra of a series of mixtures of red, green, blue, and yellow tempera (poster paints) were obtained using a Carey spectrophotometer with an integrating sphere. Points on the chromaticity diagram were obtained from the spectra, showing that whereas the mixture of yellow and blue yielded a fairly saturated green, the path of mixtures of green and red traveled on the blue side of the white point. Hence yellow is preferable as a primary color than green for tempera.

ISSN:0002-9505    

DOI:10.1119/1.11885

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

The size of the Fraunhofer diffraction pattern produced when a circular aperture is illuminated with a diverging beam of light, in contrast with a parallel beam, is derived on the basis of simple lens theory by introducing the concept of a virtual diffraction pattern. The results of the simple analysis agree with the diffraction pattern size determined by a formal analysis of the light wave amplitude. The formal analysis reveals a general scale factor relating the Fraunhofer diffraction pattern size for an aperture illuminated with parallel light to the size for nonparallel illumination. The diffraction pattern intensity is independent of the position of the aperture in its plane, based on a property of the Fourier transform. The invariance in intensity for nonparallel illumination of the aperture is also shown by a simple argument based on the Abbe theory of image formation by diffraction. Finally, some experimental results are given.

ISSN:0002-9505    

DOI:10.1119/1.11886

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

It is well known that to quantize any dynamical system it isnecessaryfor a generator of the classical motion to exist in the form of a Hamiltonian function. It is shown, by using the example of a damped harmonic oscillator, that a particular class of inequivalent classical Hamiltonians exist which make quantization of the system ambiguous. Hence it is conclued that it isnotsufficientfor the Hamiltonian to merely generate the motion, but it must also be necessarily related via a canonical transformation to the total energy of the system.

ISSN:0002-9505    

DOI:10.1119/1.11887

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

The molecular field theory of ferromagnetism is used as an example to illustrate the use of elementary catastrophe theory. It is shown that the molecular‐field approach gives rise to a cusp catastrophe set. A brief examination is made of the reasons why the elementary catastrophe theory does not produce critical exponents which are in agreement with experimental values. It is suggested that the assumption of an equal areas rule denies the transversality upon which the generality of catastrophe theory is based. It is proposed that an approach to the problem of critical exponents through the much more sophisticated generalized catastrophes might prove fruitful.

ISSN:0002-9505    

DOI:10.1119/1.11888

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP

摘要:

A particular kind of elastic scattering is studied between three bodies of equal mass. Two of the bodies are at rest and in contact with each other. The third body impinges on these two. The motion of the bodies is confined to a straight line as in a linear air track. The scattering is mediated by nearest‐neighbor Hooke’s law forces having force constantsk1andk2. The final velocities of all three bodies are studied as a function of β (=k2/k1). It is shown that the possible final scattering states may be divided into two classes. In one class it is possible to determine β from a knowledge of the final velocities of the three bodies. In the other class no such determination is possible. A formula is derived that yields an infinite set of values of β, all of which produce the same velocities in the final state. Other measurements are proposed which allow a determination of β and the individual spring constantsk1andk2as well as the size of the springs. These further measurements involve time correlations between incident and scattered particles. No measurements are permitted during the time of interaction. The correspondence principle indicates that the same ambiguity will be present in the analogous one‐dimensional quantum‐ mechanical problem necessitating time correlation measurements to solve the inverse scattering problem.

ISSN:0002-9505    

DOI:10.1119/1.11889

出版商:American Association of Physics Teachers    

年代:1979

数据来源: AIP