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?
a) by increasing the surface area between the screw surface and the wood
b) by increasing the ease of inserting the screw into the wood
c) by increasing the coefficient of static friction between the screw and the wood
d) by increasing the normal force exerted by the wood on the screw thread
d) by increasing the normal force exerted by the wood on the screw thread
Well, isn't this a twisty question! The answer is d) by increasing the normal force exerted by the wood on the screw thread. You see, when the threads of the screw are pitched at an angle, it creates a ramp-like effect, causing the wood to push harder against the screw thread. This increase in normal force leads to a greater static friction force, making it harder for the screw to slip out of the wood. It's like giving the screw a tight bear hug so it doesn't go anywhere!
The correct answer is d) by increasing the normal force exerted by the wood on the screw thread.
When the threads of a screw are pitched at an angle, it causes the screw to exert a force perpendicular to the surface of the wood. This force, known as the normal force, increases the static friction between the screw and the wood. As a result, it becomes harder to move or slide the screw within the wood, effectively increasing the static friction force.
To determine how the threads of a screw increase the static friction force when fastening two pieces of wood, we can go through the options provided.
a) Increasing the surface area between the screw surface and the wood would actually reduce the static friction force, as the friction force is directly proportional to the surface area in contact.
b) The ease of inserting the screw into the wood is not directly related to the increase in static friction force. It may affect the initial penetrating force required, but not the overall static friction force once the screw is tightened.
c) Increasing the coefficient of static friction between the screw and the wood would indeed increase the static friction force. The coefficient of static friction is a measure of how well two surfaces resist sliding past each other, and increasing this coefficient increases the friction force.
d) Increasing the normal force exerted by the wood on the screw thread would also increase the static friction force. The static friction force is directly proportional to the normal force acting on the surfaces in contact. If the screw is inserted at an angled pitch, it increases the effective normal force on the thread, resulting in an increased friction force.
Therefore, the correct answer is c) by increasing the coefficient of static friction between the screw and the wood, and d) by increasing the normal force exerted by the wood on the screw thread.