Methods for estimating moment of inertia of cricket bats

Mass moment of inertia is a key inertial property of cricket bats and should be used in selection to optimise performance. Players currently rely on a subjective assessment of how the bat feels when swung supported only by a value for bat mass from the manufacturer. This reliance on a subjective assessment is because the moment of inertia of a bat typically requires a pendulum method to measure with sufficient accuracy. In this study, two methods for estimating moment of inertia were tested. The hypotheses were that (1) an acceptable estimate of moment of inertia could be calculated using a beam model approach, and (2) the inertial property first moment could act as a proxy measure for moment of inertia. Experimental values for moment of inertia were obtained using a pendulum method. The two-section beam model showed an error of 0.43–0.53% between model and experimental values based on a Root Mean Square Error of 0.0017 kg m2. First moment data were generated on 5005 bats spread across eight bat shapes. A correlation was shown between the measured value of first moment and the beam model value of moment of inertia, with an R2 value > 0.992 for all bat shapes. This study showed that a two-section beam model and first moment method for estimating cricket bat moment of inertia could be used to improve bat selection.

Inertial property of oscillatory flow for pulse injection in porous media

The low-frequency pulse wave makes the velocity of the fluid in the reservoir fluctuate dramatically, which results in a remarkable inertia force. The Darcy’s law was inapplicable to the pulse flow with strong effect of inertial force. In this paper, the non-Darcy flow equation and the calculation method of capillary number of pressure pulse displacement are established. The pressure pulse experiments of single-phase and two- phase flow are carried out. The results show that the periodic change of velocity can decrease the seepage resistance and enhance apparent permeability by generating the inertial force. The higher the pulse frequency improves the apparent permeability by enhancing influence of inertial force. The increase of apparent permeability of high permeability core is larger than that of low permeability core, which indicates that inertial force is more prominent in high permeability reservoir. For the water-oil two-phase flow, inertia force makes the relative permeability curve move towards right, and the equal permeability point becomes higher. In other words, with the increase of capillary number, part of residual oil is activated, and the displacement efficiency is improved.

Stability Analysis and Transient Response of Electrostatically Actuated Microbeam Interacting With Bounded Compressible Fluids

This paper studies the stability and transient response of electrostatically excited microbeam interacting with bounded compressible fluid. At first, employing Fourier-Bessel series, the related eigenvalue problem of the coupled system is solved. Investigating the change in the free vibration properties of the system, a parametric study is done, accounting for changing physical properties and geometric dimensions of the bounded fluid. Then, considering the step response of the coupled system, pull-in time and voltage and also attraction zones of the microbeam are derived. It is shown that, beside the electrical property of the contained fluid, its inertial property could also change the transient response significantly. Fluid added mass by increasing the period of the free vibration response in stable condition also changes the pull-in time. In addition, it is found that the attraction zones of stable fixed points vary for different contained fluids that could change the sensitivity of the microbeam to uncertainty in the initial condition.

Modeling of Multiteeth Contact Meshing Gear Dynamics with Backlash and Coincidence Degree

In the present paper, a multiteeth meshing gear contact dynamics model is proposed by introducing a modified robotic contact model. The inertial property, backlash of gear teeth and coincidence degree of gear meshing are considered into the model. In addition, the proposed model is used to simulate discontinuous meshing gear contact. Simultaneously, the gear meshing contact dynamical finite element model is also simulated using the Ansys/LS-DYNA software to demonstrate the rationality of the proposed model.

The electrodynamics of inhomogeneous rotating media and the Abraham and Minkowski tensors. I. General theory

This is paper I of a series of two papers, offering a self-contained analysis of the role of electromagnetic stress–energy–momentum tensors in the classical description of continuous polarizable perfectly insulating media. While acknowledging the primary role played by the total stress–energy–momentum tensor on spacetime we argue that it is meaningful and useful in the context of covariant constitutive theory to assign preferred status to particular parts of this total tensor, when defined with respect to a particular splitting. The relevance of tensors, associated with the electromagnetic fields that appear in Maxwell’s equations for polarizable media, to the forces and torques that they induce has been a matter of some debate since Minkowski, Einstein and Laub, and Abraham considered these issues over a century ago. The notion of a force density that arises from the divergence of these tensors is strictly defined relative to some inertial property of the medium. Consistency with the laws of Newtonian continuum mechanics demands that the total force density on any element of a medium be proportional to the local linear acceleration field of that element in an inertial frame and must also arise as part of the divergence of the total stress–energy–momentum tensor. The fact that, unlike the tensor proposed by Minkowski, the divergence of the Abraham tensor depends explicitly on the local acceleration field of the medium as well as the electromagnetic field sets it apart from many other terms in the total stress–energy–momentum tensor for a medium. In this paper, we explore how electromagnetic forces or torques on moving media can be defined covariantly in terms of a particular 3-form on those spacetimes that exhibit particular Killing symmetries. It is shown how the drive-forms associated with translational Killing vector fields lead to explicit expressions for the electromagnetic force densities in stationary media subject to the Minkowski constitutive relations and these are compared with other models involving polarizable media in electromagnetic fields that have been considered in the recent literature.

Is It Possible to Produce Micro-Gravity in Our Own Lab?

Wouldn't it be nice to have some kind of laboratory hood in which gravity is greatly reduced so we could grow more perfect crystals or do biological experiments without having to go into orbit. There was a report in Science last year which hinted that gravity cancellation or modification just might be possible some day, but I doubt that any of our readers noticed it. The title was “Inertia: Does Empty Space Put Up the Resistance?”. One has to read this news report carefully to find that physicists have long pondered the connection between the inertial property of mass and the gravitational attraction between masses and that the work quoted here, suggests that once inertia is understood it might be controlled, even canceled. Upon inquiry the editor, Robert Matthews found other physicists believed that the ability to modify inertia could soon be tested experimentally but remarked that “it is a bit too early to be talking about inertia free star ships.”

Measurement of Mass and Cg Location of Helmet Systems

A procedure is described to measure the mass and CG location of helmet systems and relate these to head inertial properties. This procedure provides helmet mass properties data with respect to a consistent head coordinate system so that the mass properties of different helmet systems may be directly compared, allowing measurement of net head inertial property changes due to the addition of head mounted equipment. Relating helmet mass properties data to a consistent head coordinate system permits existing ejection safety criteria for head supported mass and CG location to be applied directly.