Mechanism Description

For this course, you will describe a simple mechanism with only 3-5 parts in terms of its function, its physical appearance, the appearance of each part and the relevant specifications and dimensions of both the object as a whole and its parts.

The audience for your mechanism description will be someone who is unfamiliar with the mechanism description you are describing, and needs to become familiar enough with the object to be able to distinguish it from others like it.

Formal Definitions

The first part of your mechanism description will be a formal definition of your mechanism.

A formal definition is a one to two sentence statement that does two things:

It classifies the mechanism, meaning it identifies the mechanism as a member of a group of similar objects. For instance, lead pencil is a writing instrument. Writing instrument is the class of object in which lead pencil fits.
It also differentiates the mechanism from other mechanisms that are in the same classification. For instance, a lead pencils differ from other writing instruments because they use graphite to make erasable marks. Using graphite to make erasable marks is what makes the pencil different from other mechanisms in the writing instrument category.

You will find that looking up a definition of an item in a dictionary will not always give you a workable formal definition, and for this reason it is best to be able to write a simple formal definition on your own.

Functional Definitions

The next part of your mechanism description should be a short, two-four sentence paragraph in which you describe the way your mechanism is typically used. That means, what are the functions or purposes that people fulfill with your mechanism? You do not want to advertise the mechanism, but simply describe what people do with it.

For instance, lead pencils are used for both writing and drawing. In writing applications, users favor lead pencils when erasable or non-permanent marks are needed, or when the writing is informal or subject to change. Children often use pencils when learning to handwrite because the marks can be easily erased. For drawing applications, the softness of the graphite in lead pencils lends itself well for projects in which creating shading or shadow effects are important.

Picking a Specific Mechanism

After you define your mechanism and describe its function, you need to focus the rest of your attention on a specific mechanism. Rather than describe all lead pencils, for instance, describe a Dixon Ticonderoga #2 lead pencil. By doing so, you can focus your description of its physical properties and specifications specifically.

Describing Physical Appearance

For this assignment, physical appearance descriptions should be one-two short paragraphs of five lines or less.

When you describe how something looks for someone who is not familiar with it, you need to compare the object to something your audience knows, both in terms of size and shape.

A good strategy for a physical description is to first compare your object to a familiar shape and size, and then distinguish the mechanism from what you compared it to.

It’s important to avoid using numbers or dimensions in a physical description. This advice may seem counter-intuitive, but the purpose of using words to tell someone how something looks is to create recognition. People’s perceptions of common dimensions vary much more widely than you might realize. What one person believes to be eight inches might look like 12 inches to another. To avoid this problem, discuss size in terms of similarity to known objects. Save the dimensions for the Specifications section, below.

Here is an example:

A Dixon Ticonderoga #2 lead pencil is cylinder-shaped object about the diameter of a chopstick and the length of an adult male hand from palm to the tip of the longest finger. [Notice here that the shape given is basic and that the dimensions are relative to objects that the writer believes the audience is familiar with. Since the goal of the description is recognition, we leave precision until the specifications section.]

The Dixon Ticonderoga’s body is not precisely round, but forms a hexagonal prism made of wood, in the center of which is a cylinder-shaped column of graphite approximately the same diameter the metal wire from a paper clip. [Notice how the description begins to differentiate the mechanism from the basic shape.] At one end of the pencil’s body is affixed a cylinder made of soft metal of almost the same diameter as the pencil body…

Listing Relevant Specifications

Here, you need only list the length, width, height, material types and other specifications. However, only list specifications that are relevant to the function of the object. For instance, the color of the paint on the outside of the lead pencil is probably not relevant to its function, and therefore need not be listed.

Using Page Design

Whatever the audience or purpose of a mechanism description, you need to recognize and design for the fact that it will be read selectively. That means that you will need to use specific headings and subheadings, along with bullets and other elements of page design to make your mechanism description easy to scan. Nobody reads a mechanism description from beginning to end.

See the Templates, Worksheets and Samples section for a sample of fairly successful student-created mechanism description and a student-created outline for different mechanism description that fit the assignment prompt.

A mechanism is, at its base, a man-made object consisting of two or more parts that work together in some way.

Technical writers describe mechanisms in many different ways, depending on the purpose of the description, but all descriptions come down to answering one question: What is it?

All mechanism descriptions also describe two things:

The mechanism as a whole
Some or all the parts of that mechanism

The content of mechanism descriptions varies by the context, message, audience, purpose and product desired by an audience, but some common content includes:

The appearance of the mechanism and its parts
The purpose of the mechanism and its parts
The dimensions and specifications of the mechanism and its parts
The physical properties and materials used in the mechanism and its parts
The ways in which each of the parts affect the mechanism as a whole

Mechanism descriptions occur in a variety of contexts, from design specifications to advertisements to blueprints.

Select a small, simple mechanism (3‐5 main parts) ‐ perhaps one you have worked with or will
work with in your technical area, in the science laboratory, on the job, in school, or around the
house (from your workbench, kitchen, or garage). It would be wise to select a mechanism with
which you are familiar.

Describe the mechanism as a whole and its component parts using the organizing scheme
below. Assume that the audience for this description is someone unfamiliar with both the
object and the technical terms a specialist might use to describe it. Your mechanism description
should be approximately 400‐600 words in length (about two pages). Be sure to take advantage
of headings, subheadings and the appropriate type of highlighting to aid your audience in
reading selectively.

Outline
I. Introduction

1. Define the object
2. Identify the purpose of the object

II. Description of the whole

1. Describe how the object looks (size, shape, color, texture)
2. Identify the characteristics of the object (include such details as type of material or
substance, dimensions, flammability, density, durability, expected life)

III. Description of the parts

1. Describe how each part looks
2. Identify the characteristics of each part (include such details as type of material or
substance, dimensions, flammability, density, durability, expected life)