Friction force models play a fundamental\ud role for simulation ofmechanical systems. Their choice\ud affects the matching of numerical results with physically\ud observed behavior. Friction is a complex phenomenon\ud depending on many physical parameters and\ud working conditions, and none of the available models\ud can claim general validity. This paper focuses the\ud attention on well-known friction models and offers a\ud review and comparison based on numerical efficiency.\ud However, it should be acknowledged that each model\ud has its own distinctive pros and cons. Suitability of\ud the model depends on physical and operating conditions.\ud Features such as the capability to replicate stiction,\ud Stribeck effect, and pre-sliding displacement are\ud taken into account when selecting a friction formulation.\ud For mechanical systems, the computational efficiency\ud of the algorithm is a critical issue when a fast\ud and responsive dynamic computation is required. This\ud paper reports and compares eight widespread engineering\ud friction force models. These are divided into two\ud main categories: those based on the Coulomb approach and those established on the bristle analogy.The numerical\ud performances and differences of each model have\ud been monitored and compared. Three test cases are discussed:\ud theRabinowicz test and other two test problems\ud casted for this occurrence

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The paper deals with the comparison between a high-end marker-based acquisition system and a low-cost marker-less methodology for the assessment of the human posture during working tasks. The low-cost methodology is based on the use of a single Microsoft Kinect V1 device. The high-end acquisition system is the BTS SMART that requires the use of reflective markers to be placed on the subject's body. Three practical working activities involving object lifting and displacement have been investigated. The operational risk has been evaluated according to the lifting equation proposed by the American National Institute for Occupational Safety and Health. The results of the study show that the risk multipliers computed from the two acquisition methodologies are very close for all the analysed activities. In agreement to this outcome, the marker-less methodology based on the Microsoft Kinect V1 device seems very promising to promote the dissemination of computer-aided assessment of ergonomics while maintaining good accuracy and affordable costs. PRACTITIONER’S SUMMARY: The study is motivated by the increasing interest for on-site working ergonomics assessment. We compared a low-cost marker-less methodology with a high-end marker-based system. We tested them on three different working tasks, assessing the working risk of lifting loads. The two methodologies showed comparable precision in all the investigations.