## 4 Discussion  
From the experimental results, it can be concluded that for the tested viscoelastic materials, under the conditions of the presence of substances that reduce friction (moisture, soap solution), there is a significant decrease in the coefficient of friction. The substrate conditions under which the measurements were conducted were dry, wet, and soapy. A trend of increasing friction coefficient with increasing rubber hysteresis could be observed, while the change in speed from 50 mm/s to 300 mm/s did not significantly affect the COF value. There was also a noticeable difference in the COF values between the smooth and anti-slip tiles under the same conditions, which may indicate the influence of substrate roughness as well as rubber hysteresis. The COF values were highest under dry conditions, with wet conditions showing higher COF values than soapy conditions. Figure 4A and Table 3 show that the influence of hysteresis on the COF under dry substrate conditions with the anti-slip tile was insignificant. The highest COF value was observed for the rubber with the lowest hysteresis and a hardness of 65 ShA or 60 ShA, as with the other rubber samples. The COF values under these conditions ranged from 1.2 to 1.35 at speeds of 50 mm/s and 300 mm/s, respectively. However, when water and soap were introduced, the COF dramatically dropped to values of 0.65 and 0.60 at speeds of 50 mm/s and 300 mm/s, respectively, for the rubber with the lowest hysteresis. In contrast to dry substrate conditions, in this case, an increase in hysteresis led to an increase in the COF for the same hardness, while for the highest hysteresis and a hardness of 60 ShA, the COF decreased. A similar trend was observed for the substrate in the presence of soap, but with lower COF values. The influence of rubber hysteresis was insignificant under dry substrate conditions, but it became noticeable when moisture was present in the form of soap. Rubber hysteresis had a significant influence on the COF under wet and high-speed conditions, which correspond to human walking conditions and should be considered when shoe soles are produced. If rubber hysteresis is known (tested), it is easier to predict what the COF will be for some conditions (wet, rough surface, high speed). On the smooth \begin{table}
\begin{tabular}{c c c c c} \hline
**Level** & **Hysteresis** & **Roughness** & **Speed** & **Surface Condition** \\ \hline
1 & 0.4275 & 0.2208 & 0.4238 & 0.4536 \\ \hline
2 & 0.3655 & 0.5811 & 0.3781 & 0.3483 \\ \hline
3 & 0.4550 & & & \\ \hline
4 & 0.3558 & & & \\ \hline Delta & 0.0993 & 0.3604 & 0.0456 & 0.1054 \\ \hline Rank & 3 & 1 & 4 & 2 \\ \hline \end{tabular}
\end{table} 
Table 10: Response table for means (wet, soapy). Figure 6: Main effects on COF under wet and soapy conditions. tile, there was no significant influence of rubber hysteresis on the COF. Compared to the COF on the anti-slip tile, the COF on the smooth tile was greater under dry conditions due to the influence of adhesion (the adhesive component of friction was significant), while on the anti-slip tile, the COF under wet and soapy solution conditions was greater because of the influence of hysteresis friction. The experimental results in Table 4 showed that the rubber with higher hysteresis (OB 2280) had a higher COF (for speeds of 50 mm/s and 300 mm/s) than rubbers OB221 and OB290. Also, the rubber with less hardness (60 ShA) and higher hysteresis had a lower COF in comparison with rubber OB 2280, which indicates that rubber hardness also has a significant influence on the COF. In Figure 4A, it can also be observed that the COF values under dry conditions on a smooth tile were higher than the COF values on the anti-slip tile. It can be assumed that the influence of adhesion due to a larger real contact surface was significant. In this case as well, the maximum COF values were observed for the rubber with the lowest hysteresis.