Daft as a Brush.
What is a brush? A dictionary definition includes: "A collection of fibres or bristles held in a handle or other device." That's a physical description, but it doesn't explain the concept of a brush. Let's consider a brush as a piece of technology and explore what we can use it for.
The simple act of brushing uses the bristle collection to 'sweep' unwanted materials from a surface. This may be dust from a floor, cobwebs from the ceiling or leaves from a paved area, but with different types of brush for each purpose. A stiff bristle brush is used for leaves, a small brush with shorter soft bristles for the ceiling and longer flexible fibres for the floor. There are special brushes for specific purposes. A bundle of ostrich feathers, known as a feather duster, takes on a small static charge, which makes it exceptionally good at removing dust from delicate surfaces. Use the wrong brush and you could damage the softer surfaces or fail to move many leaves. A brush may be used manually or it can be part of an appropriate machine, either stationary or on a roller or belt.
Bristles are never exactly the same length and surfaces are never completely smooth. When brushing a surface, bristles move individually, with their ends alternately catching on the surface then springing forward. This seems to give an additional push to particles as they are swept up, which helps stop them being caught up between the bristles and clogging the brush. Bristles can be made from natural or synthetic materials. Natural bristles are often tapered, varying in stiffness over their length, making them softer at the ends. Synthetic materials are usually cylindrical, with a constant stiffness along their length. They can have different lengths and thicknesses, and can be bundled in a range of densities. This allows brushes to be designed for a multitude of specific purposes, but we still take them for granted.
We can fill spaces between the bristles with liquid when we apply paint or adhesive to a surface, using our skill to produce an even distribution. This requires a softer brush, which can be manipulated to follow the shape and texture of the surface. A stiffer brush, with appropriate material, can produce textures, including stippling, swirls and patterns in the resulting surface. With a set of smaller brushes, an artist can produce the paintings which adorn our art galleries and domestic walls. In China and Japan, fine brushes are used for painting, writing and producing hieroglyphics, which don't look the same drawn with a pen. A shaving brush applies a special soap to a chin to soften hair for cutting.
Carefully designed brushes can penetrate crevices to both remove unwanted material and apply liquids, as brushing teeth or cleaning a car. They can be scrubbing brushes or used to aid washing-up. This requires a careful balance between the stiffness and flexibility of the bristles. Brushes may also be used to give a contact between a stationary and a moving surface, as in electric motors or in the brush seals resisting the drafts under your doors.
There is an odd property of some brushes. If you take a hand-brush with fairly stiff bristles ending in a flat plane, such as a clothes brush or hairbrush, you can slide it, bristles down, across a flat surface such as a table-top. It may stop quite quickly or travel much farther than you expect. This seems to be an effect of the way the bristles move. They may absorb energy as they bend or add impetus when they spring back. I have never seen this effect referred to in a technical paper. Sounds like a research project for someone.
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|Date:||Mar 1, 2018|
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