The dynamic impact characteristics of tennis balls with tennis rackets

Abstract

The dynamic properties of six types of tennis balls were measured using a force platform and high-speed digital video images of ball impacts on rigidly clamped tennis rackets. It was found that the coefficient of restitution reduced with velocity for impacts on a rigid surface or with a rigidly clamped tennis racket. Pressurized balls had the highest coefficient of restitution, which decreased by 20% when punctured. Pressureless balls had a coefficient of restitution approaching that of a punctured ball at high speeds. The dynamic stiffness of the ball or the ball-racket system increased with velocity and pressurized balls had the highest stiffness, which decreased by 35% when punctured. The characteristics of pressureless balls were shown to be similar to those of punctured balls at high velocity and it was found that lowering the string tension produced a smaller range of stiffness or coefficient of restitution. It was hypothesized that players might consider high ball stiffness to imply a high coefficient of restitution. Plots of coefficient of restitution versus stiffness confirmed the relationship and it was found that, generally, pressurized balls had a higher coefficient of restitution and stiffness than pressureless balls. The players might perceive these parameters through a combination of sound, vibration and perception of ball speed off the racket.     

The moral obligation to preserve heritage through sport and recreation facilities

The preservation of heritage through renovation projects of sport and recreation facilities is a recent phenomenon. We are not generally prompted to think of sport and recreation venues as cultural objects to preserve or as hosts to heritage, yet, they appear to be significant sources of heritage for communities and fan nations (Mason et al., 2005, Rosentraub and Ijla, 2008). Noting facilities have the ability to preserve heritage, the aim of this paper is to review contemporary philosopher Peter Singer's (1993) perspective on moral obligation to highlight the potential to protect heritage through sport and recreation facility management practices. We argue that communities and constituents may have a moral obligation to preserve heritage through sport and recreation facilities due to the value they possess. Appropriately, preservation is defined and framed as a managerial activity to assure the survival social, political, and cultural records.     

Issues in the application of a conjunctive/compensatory standard-setting model to a criterion-referenced, classroom-based teacher certification assessment system: A state case study

Wheeling Jesuit College     

Learning theories and environments: A student-initiated intelligent computer-assisted environment

Intelligent computer-assisted instructional systems have been constructed and applied within a wide range of fields. Very few of these systems make explicit a central or set of core learning theories or learning environments upon which a system is based. However, many of these systems have implicitly employed learning theories and environments. This paper looks at a variety of intelligent computer-assisted systems with a view towards uncovering the latent learning theories they employ. The interplay of the various learning theories needed to realise a student-initiated learning environment are discussed. The central features required for such an environment to function and the limitations of realising such a learning environment due to the state of the art of present day systems are also discussed. Specializations: physics education; computer education; intelligent computer-assisted instructional systems; physics problem solving. Specializations: chemical education, technology education, history and philosophy of science, learning theories.     

Prisons,old cars,and Christmas trees: A metaphoric analysis of familial communication

This paper is a metaphoric analysis that explores college students’ perceptions of their families in relation to their family of origin, concept of family, and family communication. Metaphors were thematically analyzed and placed in categories of positive, negative and neutral responses given by individuals. Constant comparative method was also used to identify themes and dimensions among the metaphors. Throughout the results, students had an overwhelmingly positive attitude toward their family of origin and the concept of family. Responses about family communication, however, tended to range mainly from a neutral to negative perception. Additional results, implications, and future directions for family communication research are also discussed.     

Journal Title Transfers: The Process,the Complexities,the Problems,and What the Transfer and KBART Working Groups are Doing to Address Them

This article examines the complicated process of journal title transfers in the electronic environment. A detailed look at summary title transfer data from the past two years outlines the untimely nature of the title transfer process. Also addressed are how two National Information Standards Organization (NISO)/United Kingdom Serials Group (UKSG) Working Groups, Knowledge Bases and Related Tools (KBART) and Transfer, are working to address some of the problems and streamline the process. Last, an automated and standardized method by which electronic holdings data could be processed is proposed for future work.     

Faculty and Librarian Perceptions of a New Faculty Purchase Program

This study explores new faculty members' and librarians' perceptions of a program that provides each new faculty member with funds to purchase materials supporting their teaching and scholarship. The article describes the results of a survey of perceptions of the faculty and librarians who have participated in the program at Illinois State University. The findings suggest that the program has not been successful as a recruitment tool but has been very valuable for establishing early and strong subject liaison relationships with new faculty members.     

Human Rights Reference Sources: A Critical Annotated Bibliography

The area of human rights has had significant attention both nationally and internationally in the press and in the political arena. While there is a renewed commitment to human rights advocacy, there is also an upward trend in popular culture of depictions of torture. This article provides critical annotations of English-language reference sources published since 1990 and available both in print and online, in an effort to aid librarians collecting and weeding materials for human rights research.     

Sent from My iPhone: The Medium and Message as Cues of Sender Professionalism in Mobile Telephony

The growing ubiquity of mobile telephony able to send e-mail raises new questions, and renews old issues, about the effect of the medium on a message. This article reports experimental results testing effects of user- and medium-generated cues on perceptions of message senders. Grounded in warranting theory, we assess the interaction of low- and high-warrant cues on perceptions of the sender's professionalism, hypothesizing senders of grammatically accurate messages are perceived as more credible. However, we also hypothesize an interaction between grammatical accuracy and the system-generated high-warrant cues from the mobile device used to send the message. Responses from 111 students assessing the credibility of an e-mail sender indicate that, although a message's user-generated content (grammatically accurate vs. erred) influences receiver's perceptions, negative attributions are attenuated by cues reflecting the transmission medium (i.e., a message's mobile signature block). Findings offer theoretical implications for warranting theory. Additionally, results suggest practitioners need to craft a message and indicate the transmission medium strategically to mitigate any impacts on attributions of professionalism to message receivers.