Page 100 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 4 Forces, Friction, and Torque (Oh My!) 81

You can see here that the W values cancel out, so cross those out. To simplify the
equation, realize that sin / cos = tan . So, the equation boils down to a simple
μ = tan . Too easy!

FIGURE 4-8 Breaking the weight into components to solve for friction (left) and revised
arrangement (right)

P roject 4-1: Estimate the Coefficient of Friction

Let’s do a quick test to get a feel for the coefficient of friction between different
materials, so you know what 5% and 40% losses look like.

Shopping List:

• Two small objects made of different materials (a 4 oz clay block and iPhone 2G
with aluminum back are used here)
• Scrap wooden board
• Protractor

• Calculator