Accelerometers used in the measurement of jerk, snap, and crackle

© 2019 Australian Acoustical Society Annual Conference, AAS 2018. All rights reserved. Accelerometers are traditionally used in acoustics for the measurement of vibration. Higher derivatives of motion are rarely considered when measuring vibration. This paper presents a novel usage of a triaxial accelerometer to measure acceleration and use these data to explain jerk and higher derivatives of motion. We are all familiar with the terms displacement, velocity and acceleration but few of us are familiar with the term jerk and even fewer of us are familiar with the terms snap and crackle. We experience velocity when we are displaced with respect to time and acceleration when we change our velocity. We do not feel velocity, but rather the change of velocity i.e. acceleration which is brought about by the force exerted on our body. Similarly, we feel jerk and higher derivatives when the force on our body experiences changes abruptly with respect to time. The results from a gymnastic trampolinist where the acceleration data were collected at 100 Hz using a device attached to the chest are presented and discussed. In particular the higher derivates of the Force total equation are extended and discussed, namely: ijerk∙d3x/dt3, rsnap∙d4x/dt4, ncrackle∙d5x/dt5 etc

Free fall and harmonic oscillations: Analyzing trampoline jumps

© 2015 IOP Publishing Ltd. Trampolines can be found in many gardens and also in some playgrounds. They offer an easily accessible vertical motion that includes free fall. In this work, the motion on a trampoline is modelled by assuming a linear relation between force and deflection, giving harmonic oscillations for small amplitudes. An expression for the cycle-time is obtained in terms of maximum normalized force from the trampoline and the harmonic frequency. A simple expression is obtained for the ratio between air-time and harmonic period, and the maximum g-factor. The results are compared to experimental results, including accelerometer data showing 7g during bounces on a small trampoline in an amusement park play area. Similar results are obtained on a larger garden trampoline, and even larger accelerations have been measured for gymnastic trampolines

Greyhound safety and welfare - A preliminary review of the Angle Park track

Presentation to the GRSA Boar

Vibration measurement as a tool to solve a murder

This paper will discuss a novel use of vibration measurement used to assist the NSW Police Force to solve the ‘pogo stick’ murder. The authors were approached by the Homicide Squad regarding a suspicious death of a 7-year boy at Oatley in May 2013. The child had reportedly fallen from a pogo stick and suffered significant head injuries. The child had not been provided with medical attention after the fall and died some 24 hours later. The incident occurred inside a small unit which was used as a music recording studio. The studio is on the first level of a larger business complex. The studio consisted of a recording room, a lounge room, and a kitchenette. The child fell in the lounge room. At the time of the alleged incident the mother was in the kitchenette, and the accused was in the recording room. According to the accused, he had headphones on and was listening to loud music when he 'felt' the vibration of the thud. Kodi Maybir was found guilty of murder in November 2015