Measurement of Friction Coefficient on a Powder Layer and Fluid Dynamic Study

Major results 1: The track in the powder layer

The tracks left in the powder layer can be classified into 3 main types as shown in Fig.4-6 (Movie 3). We distinguished these tracks by the following characteristics:

Track A. Observed near the catapult, where alternating conditions of covered and uncovered track board could be observed depending on where the disk came into contact with (hopped on) the board (Fig. 4). 
  Movie 3. The Trace in the powder layer; boundary of Trace A- B and B-C was shown. Disk had sliding from left to right.
 
 Fig. 4. Track A existing near the catapult. Disk motion from left to right.

Track B. After track A, the disk leaves a track with light impression (Fig. 5). 

 Fig. 5. Track B seen in midway of  the whole track. Disk motion from left to right.

Track C. Just before it stops, the disk plows through the powder layer and uncovers the track board (Fig. 6).

 Fig. 6. Track C observed at the end of track. Disk motion from left to right.

We do not discuss the features of  Track A because the length of Track A displayed no regularity in each experiment. Features of Track A seems to depend on factors which we can not control, for example the slope of disk at shooting and the  unevenness of the powder layer.

Traces made by light disks did not display clear boundaries between Track B and C. Track C was especially difficult to identify.

Measurement of Friction Coefficient on a Powder Layer and Fluid Dynamic Study