If indeed the friction coefficient is independent of surface area, then when I tilt them they should start to slide roughly at the same Angle.

若摩擦系数真的，与接触面积没有关系，那么两者下滑时的角度，应该基本相当。

youdao

According to the friction and wear experimental results of dry slide of carbon steel, this paper analyses the relationships between the wearing amount, types of carbon steel and load.

根据对碳素钢进行的干燥滑动摩擦磨损试验结果，对碳素钢的磨损量、磨损形态与载荷的关系加以分析。

youdao

The influences of friction coefficient of the switch slide baseplate on the actuating force, and the minimum distance between the rail and the switch rail have been analyzed.

通过建立尖轨、滑床板模型，分析了不同滑床板摩擦系数对尖轨扳动力以及基本轨与尖轨最小间隔的影响，并进行了针对性的试验。

youdao

Then there's the Slide (pictured above) which relies on interesting physics to support the iPad: a heavy high-friction rubber cylinder is pulled out of its tubular compartment under the metallic slope, and it can be placed anywhere on the slope to support the iPad at any desired angle, up to somewhere around 70 degrees -- you can see it and the others in action in the earlier video.

ENGADGET: Just Mobile talks about working with Apple and why it manufactures in Taiwan exclusively