Ancestry and country differences in intelligence test scores are a matter of heated discussion. This chapter addresses delicate issues. Even when the data are relatively clear, discussion about their interpretation and meaning easily slips into dispute. We wrote this chapter to shed light and insight instead of lightning and thunder. Our focus is the world because the issues are significant across the globe (Hunt, 2012; Jones, 2016; Rindermann, 2018). To maintain the global focus, we are not detailing data within the United States beyond what is summarized in Box 12.1. As we do throughout this book, we emphasize key research because we agree with James Flynn’s (2018, p. 128) view on this subject: “There will be bad science on both sides of the debate. The only antidote I know for that is to use the scientific method as scrupulously as possible.”

In this chapter, we begin by examining the work due to a torque. We then define the concept of the rotational kinetic energy for a point mass, systems of discrete masses, and continuous rigid bodies. We develop the angular work-kinetic energy theorem and use it to study the conservation of energy and the conservation of mechanical energy in systems involving rotational motion. To develop these theorems, we draw from our understanding of the analogous theorems in linear motion.

Pulse-width-modulated switching converters arepower circuits in which the semiconductor devicesswitch between on and off states at a rate that isfast compared to the frequencies of the input andoutput waveforms. Control of the converter isexercised by varying the ratio of on-time to totalswitching period of the controlling switches,thereby controlling the width of the pulsesapplied to the output. This is called pulse-width modulation orPWM control.

A basic understanding of device physics, andhow the physics relates to device behavior, arevaluable assets for both interpreting a device’sspecification and its successful application.

A power circuit is typically composed of only afew kinds of components (other than its source andload): switches, and energy storage elements suchas capacitors and inductors (or transformers). Inits ideal form, each of these components islossless and capable of operating at anyfrequency. In the ideal switch, for instance, thevoltage across it is zero when it is on, thecurrent flowing through it is zero when it is off,and the transition between these two states occursinfinitely fast. Although we did not explicitlydiscuss the means by which the actual switches areturned on and off (a topic covered in Chapter 23),an ideal switch responds infinitely fast to itsdrive signal and requires zero drive power.

The rectifier circuits discussed so far areuncontrollable; that is, their output voltage is afunction of system parameters and cannot beadjusted in response to parametric changes, suchas variations in load$(I_d)$ or ac voltage$(V_s)$.

The purpose of this chapter is to apply fundamentals – kinematic and dynamic analysis – in a complete investigation of a particular class of machines. The reciprocating engine has been selected for this purpose, since it has reached a high state of development and is of more general interest than most other machines. For our purposes, however, another type of machine involving interesting dynamic situations would serve just as well. The primary objective of the chapter is to demonstrate methods of applying fundamentals to the dynamic analysis of machines.

When rotational motion is to be transmitted between parallel shafts, engineers often prefer to use spur gears, since they are easy to design and very economical to manufacture. However, sometimes the design requirements are such that helical gears are a better choice. This is especially true when the loads are heavy, the speeds are high, or the noise level must be kept low.

Every experience we have leaves an imprint in our brains. Physical and social experiences can change the brain. We refer to experience because environment (1) is a catch-all term and (2) suggests that humans are passive entities. We know that this is not the case, as carefully discussed almost a century ago by Louis Leon Thurstone (1923) during the behaviorism academic tidal wave that simplified all human behavior as comprising nothing more than responses to stimuli without any role for motivation, intention, or any other nonobservable construct (Watson, 1919). With today’s historical perspective, behaviorism was much less generalized and influential than usually discussed in textbooks about the history of psychology (Braat et al., 2020). Thurstone’s active view is illustrated in the bottom of Figure 7.1. Critiquing the passive approach of behaviorism, he wrote in “The Stimulus–Response Fallacy in Psychology,”

Converter circuits in the class known asswitched-capacitorconverters (SCCs) comprise only switchesand capacitors. They operate on the principle ofcharge transfer, wherein capacitors are charged inone switching state, then reconfigured in a secondstate to deliver charge to the output. Dependingon the circuit topology and how the switches areconfigured and controlled, the converter functioncan be either step-up or step-down.

Are women smarter than men? Or is it the other way around? Other than intelligence, are other mental abilities different between women and men, and if so, do these differences matter when it comes to education, vocations, or any other practical matters? Here is the short story: women and men do not differ much, if at all, on average g-factor scores, but there are differences on certain cognitive abilities that may be relevant to education, vocational choice, and success in various walks of life. Of course, the long story is more complex and includes compelling evidence about sex differences in the brain and the basic question about where the differences come from. And there is a practical question: should any of these findings inform social and educational policy in some way?

Power semiconductor devices are distinguishedby the high current densities at which theyoperate while on, and the high voltages they mustwithstand when off. These requirements haveserious consequences for both their physicalstructure and electrical behavior. In this chapterwe consider their structural and behavioraldepartures from the ideal devices studied inChapter 16.

In Chapter 12 we introduced the process oflinearization for certain classes of nonlinearaveraged-circuit models. This allowed us to obtainLTI circuit models for small perturbations ofaveraged values from their constant values innominal, steady-state operating conditions. TheseLTI models then served as the basis for stabilityevaluation and control design in the examplesconsidered in Chapter 12.

A rectifier converts ac to dc. A basicrectifier circuit produces dc in the electricalengineering sense, that is, unipolar current flow.It does not produce dc in the mathematical sense,that is, a waveform that is constant in time andwhose spectrum consists of a single zero-frequencycomponent. A rectifier’s output containsconsiderable ac content. These ac componentsresult in fluctuations, called ripple, about the averagevalue of the dc output. Eliminating this rippleand obtaining an approximation to “pure” dcrequires insertion of a filtering process afterthe basic rectification function.