At an angle of 15◦, as shown in Fig. 7, the Teflon device shows
a larger improvement over the acrylic devices. The Teflon device
achieved 13% higher power than the acrylic with guide rail at 0.1 g,
and 70% higher power at 0.075 g. The use of Teflon versus acrylic has
a large effect at an angle because friction forces become stronger
due to the larger normal force. At the 30◦ angle in Fig. 7, the only
device that had some power output was the Teflon device because
the static friction could not be overcome by the excitation force in
both of the acrylic devices.