4.44. Screw http://www.ck12.org
4.44 Screw
- Describe a screw, and give examples of screws.
- Explain how a screw works.
- Identify the mechanical advantage of a screw.
This old chimney has a spiral staircase wrapped around it. The spiral staircase contains an inclined plane, or ramp.
Do you see it? The stairs that wrap around the outside wall of the chimney make up the inclined plane. Together
with the chimney, they represent a machine called a screw.
What Is a Screw
Ascrewis a simple machine that consists of an inclined plane wrapped around a central cylinder. No doubt you are
familiar with screws like the wood screw in the left-hand side of theFigure4.89. The cap of the bottle pictured on
the right is another example of a screw. Screws move objects to a greater depth (or higher elevation) by increasing
the force applied to the screw. Many screws are used to hold things together, such as two pieces of wood or a screw
cap and bottle. When you use a screw, you apply force to turn the inclined plane. The screw, in turn, applies greater
force to the object, such as the wood or bottle top. You can watch an animation of a turning screw at the following
URL.
http://www.learnerstv.com/animation/animation.php?ani=43&cat=physics