Results of comparison experiments

Friction coefficient obtained in the comparison experiments are shown Table 2; where m* is the friction coefficient calculated as initial velocity divided by the slide time, and where m_B is the friction coefficient for Phase B (See section 3.3). The comparison experiments were performed in July and the major experiments were done in March and July; so there were differences in the average daytime temperatures and humidity (March: 9.3 and 45 %, July: 28.8 and 48.9 %. Kyoto local meteorological observatory). Therefore results obtained July are excluded from Table 2 to eliminate the effect of temperature and humidity.

It was found the slide process contains Phase B when the powder layer is not pressed and powder can adhere to the base of the disk. The condition of surface of the track board does not influence the outcome.

Table 2. A list of experiment conditions and friction coefficients. The condition for comparison are emphasized. For the type of disk base, S is the surface which powder clings onto and M is the smooth metal surface.

condition number	kind of powder	state of powder	type of disk base	surface of the track board	m_B	m*

I	flour	not pressed	S	plywood	0.11-0.15	0.20

II-1	starch	not pressed	S	plywood	0.072-0.078	0.11, 0.14
II-1	silica sand	-	S	plywood		0.61-0.73

II-2	flour	pressed	S	plywood		0.74-1.4
II-2	starch	pressed	S	plywood		0.052-0.33

II-3	flour	not pressed	M	plywood		1.24-1.53
	starch	not pressed	M	plywood	0.064, 0.11	0.16, 0.33
	silica sand	-	M	plywood		0.39-0.72

II-4	flour	not pressed	S	galvanized iron	0.12-0.16	0.19, 0.20