QUANTIFYING HAIR MOTION 381 right-hand apex. Thus, tress shape, volume, and the homogeneity can vary during this motion. Furthermore, frequency also has a major impact on the momentum magnitude. SUMMARY/CONCLUSIONS Earlier it was noted that relatively little work has been performed in the area of hair motion. Our foundational work perhaps sheds light on this defi ciency by highlighting the com- plexity of the topic. Existing commercial equipment has been modifi ed to provide a means of controlling hair motion, for video capture and manipulation, and to provide subsequent image analysis capability. However, even with this powerful device, the com- plexity of the task in hand is still formidable. Using this equipment, we have performed systematic experiments to primarily study the amplitude of hair tress movement when oscillated in a side-to-side motion. Sizable changes in this property can occur as a function of hair treatments, experimental test conditions and considerations related the size and shape of the hair tresses being used. The nature of this motion is strongly dependent on the oscillating frequency—although the manner of this frequency response varies with the aforementioned considerations. Therefore, experiments performed at different single frequencies are very likely to produce different ranking of samples. Accordingly, we advocate the generation of amplitude versus fre- quency curves—which involve progressively and systematically increasing the oscillating frequency. The relationship between frequency and energy allows for conceptualization of hair move- ment in terms of the amount of motion attained as a function of energy input to the system. For example, visibly diminished motion as a result of silicone oil treatment is accompa- nied by both a reduction in the motion amplitude and an increase in the frequency neces- sary to produce this motion (i.e., lesser motion, even though additional energy is being supplied to the system). Conversely, it can be suggested that improved movement might involve enhanced motion for a given energy input, and/or comparable motion for less energy input. Figure 9. Analyzing hair shape and fl yaway during motion.

JOURNAL OF COSMETIC SCIENCE 382 A further important factor appears to be the shape of the hair during motion. For example, clean, healthy hair tresses tend to rhythmically “pulse” during the sinusoidal motion— with the extent being dependent on factors such as hair shape, tress conformation, fre- quency, etc. The goal of this work was to establish a method for numerically describing hair motion— and our approach yields a myriad of such numbers. We recognize that the nature of hair motion is highly frequency dependent and so comparisons necessitate systematic experi- ments performed across a range of conditions. For each of these conditions, it is then pos- sible to quantify an amplitude of motion and values describing the hair shape of moving hair. Thus, we quickly end up with a sizable amount of data—which seemingly provides the most insight when compared holistically. It appears reasonable to suppose that motion is dictated by a variety of single fi ber properties—for example, weight, stiffness, and interfi ber friction. Therefore, validation-type experiments have used treatments that infl uence such properties. However, specifi c treat- ments tend to not alter just one property. For example, surface lubrication might be attained in combination with increased hair weight fi ber stiffness might increase in combination with lesser friction. This severely complicates attempts to understand the effect of any single variable on the shape of our amplitude versus frequency curves. Our work continues in an attempt to best elucidate which of these now measurable prop- erties best equates to visual observation. REFERENCES (1) A. Galliano, M. Lheur, and R. Santoprete, Analysing the movement of a hair swatch using video and image analysis: a promising technique for exploring the dynamic properties of hair, Int. J. Cosmet. Sci., 37(1), 56–62 (2015). (2) P. S. Hough, J. E. Huey, and W. S. Tolgeshi, Hair body, J. Cosmet. Sci., 27, 571–578 (1976). (3) C. R. Robbins and G. V. Scott, Prediction of hair assembly characteristics from single fi ber properties, J. Cosmet. Sci., 29, 783–792 (1978). (4) S. Breugnot, M. Vedel, R. George, K. Nowbuth, and P. Sterle, Volumizing, fl y-away/frizz control and straightening claim substantiation using 3D volume measurement system, NutraCos-Anno, 7(2), 9–14 (2017). (5) T. A. Evans, “Chapter 10: Adsorption Properties of Hair,” in Practical Modern Hair Science, T. A. Evans and R. R. Wickett. Eds. (Allured Books, Carol Stream, IL, 2012).