George Barnes

Liquid Rope-Coil Effect

The tendency for a falling stream of very viscous liquid to coil like a rope when it strikes a horizontal surface is studied and the building of a “cone” of liquid of considerable height above the surface is observed. It is shown that, although the liquid stream as a whole appears to rotate about the axis of the “cone,” the particles of liquid do not actually rotate about this axis. Variations of the liquid rope-coil effect are discussed.

Study of Collisions. Part. I. A Survey of the Periodical Literature

A review of the periodical literature on the subject of impact and the coefficient of restitution e shows that it depends not only on the materials (elastic moduli) of the colliding objects, but also on (1) their relative normal velocity at the instant of impact, (2) their shapes and sizes, (3) their masses, and (4) the medium in which the impact occurs.

Scores on a Piaget‐type questionnaire versus semester grades for lower‐division college physics students

A study involving 338 students in six different lower‐division physics courses is reported in which students’ Piagetian levels of intellectual development as determined by a written questionnaire versus final semester grades are compared. A good correlation would provide the instructor with a useful counseling tool while a poor or zero correlation would not. In either case, the questionnaire results can guide the selection of instructional materials and techniques for the class. The correlation coefficients were found to be positive, but low, for the grades A, B, and C, and the statistical scatter diagrams show a wide spread of Piagetian levels of intellectual development within each letter grade level. Other factors than the ability to think logically appear to be of greater importance for the D group, and no correlation can be seen for the W’s and F’s. The wide spread of Piagetian levels of thought for each grade level suggests that students can somehow attain passing, if not high, grades in the more el...

Height of Fall Versus Frequency in Liquid Rope-Coil Effect

When height of fall is plotted against frequency of coiling in the liquid rope-coil experiment a straight line relationship that does not pass through the origin results. A correction due to the effect of surface tension on the stream of falling liquid yields “effective” heights of fall which, when plotted against the rate of coiling, does result in a straight line through the origin.

Study of Collisions. Part II. Survey of the Textbooks

A survey of physics and engineering textbooks indicates that there is lack of agreement among the authors on the subject of impact and the coefficient of restitution as well as disagreement between the textbook authors and the writers of the articles in the periodicals. The confusion arises primarily because of (1) the way in which the coefficient of restitution e is so often defined, (2) the nature of the usual discussions of it, and (3) the reason given for e being less than unity for most collisions between objects of ordinary size. Ways of eliminating the difficulty are discussed.

Physics in Auto Accidents

This article concerns a particular application of the fundamentals of physics with which most physicists have little contact. Some elementary physics commonly used by our law enforcement officers in the reconstruction of automobile accidents is reviewed. In particular, formulas for the determination of (a) vehicle speed through skid marks, (b) minimum speed for a vehicle skidding off-course while turning a corner, (c) minimum speed required to roll a vehicle over sideways, and (d) center of mass are discussed.

Hatchet or Hacksaw Blade Planimeter

The hatchet or hacksaw blade planimeter, consists only of a sharpened pointer, a rigid arm, and a knife edge. Its theory was first given by F. W. Hill in the Philosophical Magazine in 1894 and was later simplified by Satterly. Hill and Satterly showed that the numerical value of the area within a closed curve traversed in the proper manner by the pointer is equal to the product of the length of the planimeter arm and the net displacement suffered by the knife-edge as measured along an arc with the pointer at the center of curvature. The present paper gives a relatively simple derivation yielding essentially the same result but using an entirely different method of approach. It is also shown that the procedure for operating this planimeter can be simplified when determining areas within certain types of closed curves. The accuracy of the planimeter is discussed.

Addition to the Ballistic Pendulum Experiment

An addition to the elementary ballistic pendulum experiment is described. The basis of the addition is the use of a pump-action pellet gun of accurate bore whose projectile can be fired at a relatively small velocity. By determining the drop of the projectile over a horizontal distance of about 40 ft, its muzzle velocity can be calculated. Comparison of results with those of the usual experiment gives rise to errors of 5% or less.

The two cycles of the rotary Curie‐point heat engine

The behavior of a heat engine’s working substance, as it passes through a set of thermodynamic processes and returns to its original state, is called its cycle. Most heat engines have a single cycle, and, for most, the working substance is steam, a gas, or a gas–vapor mixture. The Curie‐point heat engine is a solid‐state device having only one moving part in which two simultaneous cycles occur, but neither needs to involve a gas or vapor. One cycle describes work done by a magnetic torque τ, which causes an angular displacement θ. The second is a hysteresis cycle of magnetic field intensity H and intensity of magnetization M. Some positive and some negative work is produced during both cycles.

The three‐dimensional hysteresis surface for nickel

The sizable temperature change that the ferromagnetic working substance of a Curie‐point heat engine undergoes during each cycle makes the hysteresis loop lie on a three‐dimensional surface in magnetic field intensity (H), intensity of magnetization (M), and temperature (T) space. The surface is on the inside of a completely enclosed cavity that contains all possible one‐, two‐, and three‐dimensional hysteresis curves and loops for the element nickel, under normal conditions. The saturation curves are within two infinitely long ‘‘cracks’’ of finite width. Photographs of a three‐dimensional scale model of half of the symmetrical cavity for the element nickel are shown. Simple theorems are developed for easy calculation of the work done and the heat transferred along a segment of any three‐dimensional hysteresis curve in HMT space.