In the current study, the coefficient of static friction was measured by quantifying the maximum achievable angle, (16) and the coefficients of friction for the running shoes were within the range of data reported in previous studies.

Coefficients of friction and free moments that are too low may cause a slippery shoe-floor interaction, resulting in increased risk of fall (22) and decreased quality of performance.

As running and sidestepping are commonly performed in dance, sufficient coefficients of friction and free moments are needed to prevent falls and maintain dance performance.

1 is used to calculate coefficients of friction from the measured force and known mass of the test sled.

This test method was developed by modifying a standard torsional rheometer (RSM 800 from Rheometrics), so that the torque required to rotate one polymer surface across another contacting polymer surface could be measured and converted into coefficients of friction [18].

The results showing the variations in coefficients of friction with temperature as measured by the two test techniques are illustrated in Figs.

The results at different coefficients of friction are very similar and the difference between them is less then 5 %.

But the change of values for elongation and reduction of area measured at different coefficients of friction is even smaller (less than 5%) than the change of tensile and yield stresses.

One of the reasons for very small difference in mechanical properties when using different lubricators with different coefficients of friction could be the fact that we have done our experiments with lubricant with rather low coefficients of friction [mu] (between 0,05 and 0,16).

These materials have lower

coefficients of friction and higher useable service temperatures than engineered thermoplastic materials.

The coefficients of friction decreased with increasing pressure for all resins.

The coefficients of friction for these resins increase with increasing velocity, and thus for a given pressure and temperature the coefficient will be higher at the barrel interface than at the screw root interface.