Volume 20, Issue 9, 01 September 1949
Index of content:
20(1949); http://dx.doi.org/10.1063/1.1698540View Description Hide Description
The aerodynamic forces on golf balls were studied by dropping spinning balls through the horizontal wind stream of the B. F. Goodrich wind tunnel. The lift,L, and drag,D, were calculated from the drift of the balls, rotating at speeds, N, up to 8000 r.p.m. while falling through a wind stream having a velocity of 105 feet per second. For a standard dimple or mesh golf ball weighing 0.1 lb., the lift varied with the rotational speed as L=0.064 ×[1−exp(−0.00026N)], with a maximum observed value of 0.055 lb. or more than half the weight of the ball. The drag increased nearly linearly from about 0.06 lb. for no spin to about 0.1 lb. at 8000 r.p.m.
For a smooth ball the lift was negative at all rotational speeds below 5000 r.p.m. Above this speed, the lift was positive but was less than for the standard ball. The drag for these balls was nearly constant at about 0.08 lb. Balls with shallower dimples than standard gave intermediate results. Driving tests were consistent with the wind tunnel results.
These results explain why a golfer cannot obtain long drives with a ball having a smooth surface and why the standard dimple or mesh surface gives him greater distance and better control of the ball.
20(1949); http://dx.doi.org/10.1063/1.1698541View Description Hide Description
A discussion of the use of the wave addition method for making projections of the crystal structure factor, Fhko , upon the reciprocal lattice, in a fashion similar to that used in making electron density projections in real space, through the use of the ``sand machine'' and devices operating on similar principles, has been developed.
20(1949); http://dx.doi.org/10.1063/1.1698542View Description Hide Description
Theoretical models of antennas driven by hypothetical generators are contrasted with antennas driven from transmission lines. The coupling between an antenna and a two‐wire line driving it, as well as end‐effects on the line, are considered in their relationship to the definition of an independent impedance for the antenna. It is concluded that a physically significant impedance can be defined only outside a terminal zone near the junction of load and line. The derivation and approximate solution of generalized transmission‐line equations that take account of coupling‐effects and end‐effects are given for (1) antenna as end‐load in the plane of a two‐wire line with and without a high impedance‐stub support; (2) antenna as center‐load in the plane of a two‐wire line symmetrically driven at each end; (3) antenna as end‐load in the plane perpendicular to the line with stub support. Theoretical predictions of measured impedances defined outside a terminal zone on a feeding line in these several arrangements may differ greatly from one another and from the ratio of scalar potential difference to current for an isolated antenna with gap. These differences are due primarily to capacitive end‐effects and coupling‐effects of which account may be taken by a lumped positive or negative capacitance across the load terminals of an ideal transmission line. Inductive effects are also involved but are relatively small. Methods for evaluating the elements in a terminal‐zone network are given. The theoretical results are verified experimentally with good agreement in all cases.
20(1949); http://dx.doi.org/10.1063/1.1698543View Description Hide Description
Space charge free potential functions for a particular type of thermionic vacuum tube are derived and represented graphically for four sets of boundary conditions. The geometry under consideration comprises two spaced parallel equipotential metallic planes between which are three symmetrically interposed planes of spaced metallic strands. The strands are mutually parallel in their respective planes, though the strands in planes adjacent to the equipotential surfaces are both orthogonal to those in the central plane. This structure is divided principally into two planes, due to the orthogonal relationship between the strands in the central and adjacent planes. These two planes are each conformally transformed such that the analysis thereof yields the desired potential functions for the original structure, neglecting edge effects. Finally, the theoretical results are applied to a typical commercial thermionic vacuum tube.
20(1949); http://dx.doi.org/10.1063/1.1698544View Description Hide Description
Computations of the free energy of some chemical reactions involving dissociation or reduction of alkaline earth oxides have been made on the basis of rough estimates of the thermochemical quantities which have not been measured. The resulting values of free energy,equilibrium constant and equilibrium pressure of barium vapor derived for specified ideal conditions are tabulated. Several applications of these results are discussed.
20(1949); http://dx.doi.org/10.1063/1.1698546View Description Hide Description
A typical system for measuring pressures in a rarefied gas consists of a vacuum gage connected to the gas by a length of tubing, usually with an orifice of diameter smaller than that of the tubing at the end. The interior surface of this system will outgas at a fairly constant rate for a long period of time so that an equilibrium state will be reached with a definite non‐constant pressure distribution along the tubing. The response time constant for the system to come to equilibrium and the difference in pressure between gas and gage are functions of the outgassing rate and the geometry of the system. An analysis is made assuming molecular flow, and formulas are obtained for the response time and the pressure difference. It is shown that there is an optimum value of the tubing diameter for a given orifice diameter, gage volume, and length of tubing. This optimum is rather critical; if the diameter is too small, response time constants of the order of hours may result. Experimental work has been done and the results compared with theory. This work was done under ONR contract.
20(1949); http://dx.doi.org/10.1063/1.1698547View Description Hide Description
A generalization of Nyquist diagrams is developed. These new diagrams yield a lower limit to the values of ``damping ratios'' and so permit the evaluation of the stability and the ``degree'' of stability of systems characterized by ordinary linear differential equations.
20(1949); http://dx.doi.org/10.1063/1.1698548View Description Hide Description
20(1949); http://dx.doi.org/10.1063/1.1698549View Description Hide Description
The boundary value problem involved in finding the propagation characteristics of electromagnetic waves in a cylindrical tube containing a coaxial d.c. discharge is solved. Ohm's law is assumed to hold for the alternating current. This assumption has been verified theoretically for the case where the alternating electric field is small compared with the d.c. field. Curves which give the relationship between the complex propagation constant, γ, and the complex dielectric coefficient, Kc ′, have been computed for the solution in which the TEM mode of the coaxial line is approached as Kc ′ becomes infinite.
20(1949); http://dx.doi.org/10.1063/1.1698550View Description Hide Description
It has been observed that the microwave power loss of a section of wave guide filled with ironpowdermaterial could be varied by subjecting the ironpowder to an externally applied magnetic field. This paper describes some experiments performed with various kinds of ironpowders. Measurements have been made with the magnetic field applied parallel to, and perpendicular to the plane of the magnetic component of the electromagnetic wave inside the guide. The possibility of ferromagnetic resonance is considered. A theoretical formula for the power loss exhibited by low conductivity ironpowder attenuators is developed and compared with experimental measurements.
20(1949); http://dx.doi.org/10.1063/1.1698551View Description Hide Description
20(1949); http://dx.doi.org/10.1063/1.1698553View Description Hide Description