Rosly Jaafar

Mechanical Efficiency of a Mass-Spring System in Hypergravity, Normal Gravity and Microgravity

The operation of a mechanical machine may behave differently in various gravitational conditions. We compare the mechanical efficiency of a mass-spring system in three different gravitational conditions, namely hypergravity (2G), normal gravity (1G) and microgravity (0G) through parabolic flight. The simple system consisted of a mass load (18.92 g and 21.97 g) attached between two springs 6.91 N/m which make overall length 410 mm. The mechanical efficiency is justified by the decay of the oscillation amplitude of the attached load. Our result shows that the mechanical efficiency for the simple mass-spring system is better in lower gravitational condition.

Elastic constant determination of hardwoods using ultrasonic insertion technique.

HighlightsInsertion technique is used to determine elastic constant of hardwoods.Elastic constants are determined in longitudinal, tangential and radial directions.Twelve Malaysian hardwoods are used to validate the use of insertion technique.Results from insertion technique are compared with through‐transmission technique. ABSTRACT Ultrasonic insertion technique (IT) is an ultrasonic technique which involves sample immersion in a solution to determine its acoustic properties. IT is normally used to determine the acoustic properties of a medical phantom. We proposed the use of IT as an alternative technique to the common contact ultrasonic technique: through‐transmission technique (TT) for determining the elastic constant of hardwoods in longitudinal, tangential and radial directions. The elastic constant of twelve rectangular‐shaped Malaysian hardwoods from three different categories; heavy, medium and light with the density ranging from 602 to 992 kg m−3 were determined using IT and TT. Both techniques were carried out at 24.0 °C surrounding temperature and utilized 2.25 MHz ultrasonic transducers. Data from both techniques were compared to validate the use of the proposed technique. Findings indicated that IT offers consistent and accurate results for, tangential and radial elastic constants (TEC and REC) within 8.89% and 5.86% differences, respectively compared to TT for all tested hardwoods. IT offers an alternative technique for TEC and REC determinations of precious wood samples.

Acoustic Characterisation of Konjac Glucomannan Gel as a Medical Phantom

Acoustic properties are the main criteria to evaluate the compatibility of tested materials as a medical phantom. We determined the acoustic properties of konjac glucomannan (KGM) gel to verify its compatibility as a medical phantom. The acoustic properties measurement employed ultrasonic insertion technique and utilized two identical transducers of 5 MHz center frequencies. One KGM gel block with 5.62 mm thickness was used as sample to determine its longitudinal speed, acoustic impedance and attenuation coefficient at three different water temperatures; (21.5 ± 0.1), (22.5 ± 0.1) and (23.5 ± 0.1) °C. Findings indicated that its longitudinal speed and acoustic impedance increased from (1495 ± 1) to (1499 ± 1) m s-1 and (1.555 ± 0.001) to (1.559 ± 0.001) × 106 kg m-2 s-1 as the water temperature increased from (21.5 ± 0.1) to (23.5 ± 0.1) °C. It also indicated that its attenuation coefficient varied around (0.1303 ± 0.0107) to (0.1373 ± 0.0103) dB cm-1 with increasing water temperature. KGM gel is compatible to be a medical phantom since its acoustic properties are comparable to the acoustic properties of human soft tissue.

Visualization of Harmonic Series in Resonance Tubes Using a Smartphone

Because sound waves are such an abstract concept in physics, hands-on activities are often recommended to improve students’ understanding and strengthen their knowledge. However, most schools do not have sufficiently sophisticated measuring instruments to perform sound wave experiments. Recently, researchers used smartphones as oscilloscopes, signal generators, and spectrum analyzers for sound wave experiments. Here we provide a complement to these ideas, developing an affordable smartphone-based sound wave experiment kit to visualize the harmonic series in resonant tubes. It is based on Kundt’s tube, which was originally used to determine the mechanical properties of unknown metal rods and acoustical properties of gases. We also use it to demonstrate the difference in particles’ distribution in harmonic series in both-closed-end, one-closed-end, and both-open-end tubes.