Question

the threads of a screw used to fasten two pieces of wood are pitched at an angle. how does this increase the static friction force? (1 point)
by the normal force exerted by the wood on the screw thread
by increasing the normal force exerted by the wood on the screw thread
by decreasing the coefficient of static friction between the screw and the wood
by increasing the ease of inserting the screw into the wood

Explanation:

The formula for static friction force is \(F_f=\mu_sF_N\), where \(\mu_s\) is the coefficient of static friction and \(F_N\) is the normal force. When the threads of a screw are pitched at an angle, it causes the wood to exert a greater normal force (\(F_N\)) on the screw thread. Since \(F_f\) is directly proportional to \(F_N\) (assuming \(\mu_s\) remains constant), increasing \(F_N\) increases the static friction force.

• Option 1: Just stating the normal force exists is not enough; it's about increasing it.
• Option 3: Decreasing \(\mu_s\) would decrease \(F_f\), which is wrong.
• Option 4: Ease of inserting (related to lower friction) is opposite of what we want (increasing static friction).

Answer:

By increasing the normal force exerted by the wood on the screw thread.