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The author describes a physics experiment designed to illustrate Isaac Newton's principle that for every action there is an equal an opposite reaction. This demonstration uses a magnet falling through a conducting tube without touching it and a spring scale that reads reaction force.

This article focuses on an examination of the Kounin-Lewin theory. According to the Kounin-Lewin theory, two processes operate side by side in mental development. As one grows older, and learning presumably occurs, the capacity for diverse kinds of activity increases toward a maximum. That is, differentiation, as measured by an intelligence test, increases toward a maximum with increasing age. Simultaneously another process is at work. As one grows older, the boundaries between regions of the psychological structure of a person become resistant to modification. This is, rigidity increases with age. If rigidification develops at a greater rate than differentiation, an individual will be retarded.

The article focuses on variability in perceptual dimensions. The present study is an investigation of the differential variability of four dimensions of perception: discrimination, apprehension, comprehension and interpretation. The background for the problem is found in the different ways of investigating personality through perception. Researcher Else Frenkel-Brunswik has described the main alternatives as the "perception-centered" and the "personality-centered" approaches. Briefly, the perception-centered studies seek to describe relationships between perceiving and antecedent conditions. Alternatively, the personality-centered investigations describe relationships between personality traits and perceiving. The former search for the general laws, the latter for the kinds of individual differences in perception. Alternatively, however, the two approaches may be combined. To achieve such a synthesis, the first step is to establish the independent dimensions of perception. The second step is to investigate the kinds of variation in these dimensions as antecedent conditions were varied.

Precision agriculture accounts for within-field variability for targeted treatment rather than uniform treatment of an entire field. It is built on agricultural mechanization and state-of-the-art technologies of geographical information systems (GIS), global positioning systems (GPS) and remote sensing, and is used to monitor soil, crop growth, weed infestation, insects, diseases, and water status in farm fields to provide data and information to guide agricultural management practices. Precision agriculture began with mapping of crop fields at different scales to support agricultural planning and decision making. With the development of variable-rate technology, precision agriculture focuses more on tactical actions in controlling variable-rate seeding, fertilizer and pesticide application, and irrigation in real-time or within the crop season instead of mapping a field in one crop season to make decisions for the next crop season. With the development of aerial variable-rate systems, low-altitude airborne systems can provide high-resolution data for prescription variable-rate operations. Airborne systems for multispectral imaging using a number of imaging sensors (cameras) were developed. Unmanned aerial vehicles (UAVs) provide a unique platform for remote sensing of crop fields at slow speeds and low-altitudes, and they are efficient and more flexible than manned agricultural airplanes, which often cannot provide images at both low altitude and low speed for capture of high-quality images. UAVs are also more universal in their applicability than agricultural aircraft since the latter are used only in specific regions. This study presents the low-altitude remote sensing systems developed for detection of crop stress caused by multiple factors. UAVs, as a special platform, were discussed for crop sensing based on the researchers' studies. [ABSTRACT FROM AUTHOR]