摘要:

The radiation pressure is calculated for a surface which is moving in an electromagnetic radiation field that is isotropic to a rest observer. In the limit where the velocity of the surface is that of light, the pressure is found to reach a maximum value 2u, whereuis the isotropic electromagnetic energy density for the observer at rest. The finite value comes with an integration over radiation incident at all angles, even though radiation from a source which is directly approaching the surface has infinite momentum when the surface velocity reaches the speed of light. Estimates of radiation pressure in interstellar space lead to the result that the energy expended by a space-traveling vehicle in moving against electromagnetic radiation, at any possible speed, would be negligible.

ISSN:0002-9505    

DOI:10.1119/1.1935956

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

A brief discussion of the advantages of punched cards for personal filing systems is given, followed by a description of the system used by the author.

ISSN:0002-9505    

DOI:10.1119/1.1935957

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

In order to teach modern microphysics successfully it has been found necessary for the students to make their own vacuum tubes. But making vacuum tubes by standard techniques involves an expenditure on equipment of many thousands of dollars and the services of highly skilled technicians. A research program has been carried out which resulted in a technique whereby students can make their own vacuum tubes by using a Meccano-like kit of parts at a cost of a few tens of dollars per kit. No skilled technicians are necessary and high vacua (10−7to10−8mm Hg) are obtained without the customary precautions as to cleanliness and without costly equipment. Two methods of exhaust are used: (1) A method using activated charcoal,CO2, a special gettering regime, and a vacuum gauge. (2) A method using a mechanical pump with the same gettering regime and vacuum gauge. A students' kit has been designed and exhibited. Some classroom experiments have been demonstrated. The vacuum technique and kits have applications in research and industry as well as in teaching. This project is being carried out at the request of Professor Jerrold R. Zacharias in connection with the new physics course of the Physical Science Study Committee of Educational Services Inc.

ISSN:0002-9505    

DOI:10.1119/1.1935958

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

The impact ball apparatus, which usually consists of a straight row of balls of equal size touching each other, is used for demonstrating conservation of momentum. If the balls are perfectly elastic and there are more than two balls in the row, then ifNballs are drawn aside and allowed to strike the remaining group, it is-just not true, as is often erroneously supposed, thatNballs fly out from the other end of the row while the other balls remain at rest. The two principles of conservation of momentum and of energy are sufficient to determine the motion after impact of only two balls. If there are more than two, then the law of force between the balls (a32power law) must be invoked. The case for three equal masses withlinearforce laws is solved exactly and several consequences are discussed. Numerical solutions for the cases of three and four equalspheresare given. Calculations are found to agree with experimental data. When a single ball of velocityv0impacts against two balls in contact at rest, the velocities after impact are−0.0710v0,+0.0765v0, and+0.9944v0, if the balls are elastic. Since the demonstration is always interesting and has many ramifications, it seems unnecessary to mislead students into believing that the velocities of the balls with relatively little motion arise because of inelasticity or misalignment, neither of which can explain the negative velocity. If the coefficient of restitution is much less than unity, then inelasticity masks the effects discussed here.

ISSN:0002-9505    

DOI:10.1119/1.1935959

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

A discussion of virtual binding and resonance scattering is presented in such a fashion as to make clear the relationship between them.

ISSN:0002-9505    

DOI:10.1119/1.1935960

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

If the Hamiltonian contains nonquadratic terms, the energy contribution per particle and degree of freedom deviates from12kT(classical approximation). A very simple case which can be easily treated is that of a particle in a sinusoidal potential field. Energy, free energy, and molar heat are calculated as an example of the resulting deviations from equipartition.

ISSN:0002-9505    

DOI:10.1119/1.1935961

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

This after-dinner address attempts to point up in a simplified way the amusing, as well as some of the more serious, problems which arise in connection with flight into space. Figures are given to challenge some of the more fanciful claims about the value of the moon as a military base, noting the very large amounts of fuel required to take weapons up to the moon and then to return them to the earth. Some of the important research problems in physics and astronomy which can be carried out by the use of space vehicles are enumerated. As examples of a space science enterprise, the results of the magnetic field measurements by the Pioneer V package are summarized. The impractibility of using the moon and other planets as colonies for the earth's excess population is also demonstrated.

ISSN:0002-9505    

DOI:10.1119/1.1935962

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

Despite the fact that the study of electrostatics has been carried on for centuries, the problems as to why there is a transfer of electricity when dissimilar substances are rubbed together and how this transfer is facilitated by the rubbing process have not been answered satisfactorily. In this paper some experimental work in electrostatics which gives results in contradiction to the treatment of this topic, given in many elementary text books of physics, is described.

ISSN:0002-9505    

DOI:10.1119/1.1935963

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

The properties of plane electromagnetic waves are derived without the use of calculus in a manner which provides a fundamental understanding of isolated waves far removed from their sources or any guiding conductors. The symmetrical relationship of the induced electric field to the induced magnetic field and the role of the displacement current are clearly demonstrated. Expressions for the velocity of the wave and the magnitudes and directions of the fields are derived. These results are developed directly from basic induced field concepts, thus avoiding the complications arising in the traditional transmission line approach which of necessity involves free charges and conduction currents.

ISSN:0002-9505    

DOI:10.1119/1.1935964

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP

摘要:

A general, rigorous method is presented for obtaining the equation for the speed of light in a flowing liquid. The derivation leads to an expression correct to all orders in the ratio of the speed of the liquid to the speed of light in a vacuum. The procedure used is based on establishing a differential equation which relates the light frequency to the speed of the liquid. Comparison is made between this general approach and the more usual approach. Limitations of the usual approach are discussed.

ISSN:0002-9505    

DOI:10.1119/1.1935965

出版商:American Association of Physics Teachers    

年代:1960

数据来源: AIP