Screw

Claudia Alaniz, Jaelynn Artis

Explanation

The screw either holds something's together or drives then apart. It is a simple machine that works as a modified incline plane. As the screw is turned, the screw enters deeper into the substrate.

One example

Once inside the substrate, the frictional force of the thread is intended to prevent the screw from rotating back out of the substrate.

One example

The slope of the screw is the distance for one complete rotation around the screw while the height of the inclined plane is the distance between the threads, known as pitch.

Mechanical advantage

A screw is used in assessing the performance of a machine by dividing the circumference of the screw by the lead of the screw.

Example problem

  1. Measure the pitch of the screw. The pitch of the screw is the distance between the threads and is determined by measuring the number of threads per inch (or centimeter) on the screw then dividing one by the number of threads (pitch = 1 / number of threads per inch or cm). For example, if a screw has eight threads per inch, the pitch is 1/8.
  2. Measure the circumference of the screw. Circumference is calculated by measuring the diameter of the screw and multiplying by pi (circumference = diameter of the screw x pi). For example, if a screw has a diameter of 0.25 inches, then the circumference of the screw is 0.79 inches (0.25 inches x 3.14 = 0.79 inches).
  3. Calculate the mechanical advantage of the screw by dividing the circumference of the screw by the pitch of the screw. Using the previous examples, a screw with a pitch of 1/8 and a circumference of 0.79 inches would produce a mechanical advantage of 6.3 (0.79 inches/ 0.125 = 6.3).
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Screw in action