Human hands sweat in different circumstances and the presence of sweat can alter the friction between the hand and contacting surface. It is therefore important to understand how hand moisture varies between people, during different activities and the effect of this on friction.In this study a survey of fingertip moisture was done. Friction tests were then carried out to investigate the effect of moisture.Moisture was added to the surface of the finger, the finger was soaked in water, and water was added to the counter-surface; the friction of the contact was then measured. It was found that the friction increased, up until a certain level of moisture and then decreased. The increase in friction has previously been explained by viscous shearing, water absorption and capillary adhesion. The results from the experiments enabled the mechanisms to be investigated analytically. This study found that water absorption is the principle mechanism responsible for the increase in friction, followed by capillary adhesion, although it was not conclusively proved that this contributes significantly. Both these mechanisms increase friction by increasing the area of contact and therefore adhesion. Viscous shearing in the liquid bridges has negligible effect. There are, however, many limitations in the modelling that need further exploration.

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We performed experiments in which a soccer ball was launched from a machine while two cameras recorded portions of its trajectory. Drag coefficients were obtained from range measurements for no-spin trajectories, for which the drag coefficient does not vary appreciably during the ball's flight. Lift coefficients were obtained from the trajectories immediately following the ball's launch, in which Reynolds number and spin parameter do not vary much. We obtain two values of the lift coefficient for spin parameters that had not been obtained previously. Our codes for analyzing the trajectories are freely available to educators and students.

Ridges are often added to surfaces to improve grip of objects such as sports equipment, kitchen utensils, assistive technology, etc. Although considerable work has been carried out to study finger friction generally, not much attention has been paid to understanding and modelling the effects of surface texture. Previous studies indicate that at low roughness values friction decreases as roughness increases, but then a sharp increase is seen after a threshold level of roughness is reached. This is thought to be due to interlocking. In this study an analytical model was developed to analyse the different mechanisms of friction of a fingerpad sliding against triangular-ridged surfaces that incorporated adhesion, interlocking and hysteresis. Modelling was compared with experimental results from tests on five different triangular-ridged surfaces, manufactured from aluminium, brass and steel. Model and experiment compared well. The study showed that at low ridge height and width the friction was dominated by adhesion. However, above a ridge height of 42.5 m, interlocking friction starts to contribute greatly to the overall friction. Then at a height of 250 m, a noticeable contribution from hysteresis, of up to 20 % of the total friction, is observed.

Gripping is an everyday task which is taken for granted by many. The current paper examines extant knowledge of howobjects are gripped for manipulation, and the relationship, the coefficient of friction, between finger and object, has on various grip parameters. It is found that friction is an essential part of the feedback and feedforward control system for grip. The friction of the finger-object contact can be measured in several different ways, using methods of either a probe moving on a finger or a finger moving on a flat surface. These friction measurements can then be used to gain information about the effect of normal force, sliding speed, contact area, and level of moisture present. They also can provide information about the changes between test subjects, for example, the effects of age, gender, and race. Knowing the effect of these parameters can help to improve the manoeuvrability of everyday items through inclusive design; designing products to be used by the whole population regardless of age or ability. The current paper also suggests areas of further investigation so that knowledge of skin friction can be expanded and applied to a larger range of materials and applications.