Blade

A blade is the portion of a tool, weapon, or machine with an edge that is designed to cut and/or puncture, stab, slash, chop, slice, thrust, or scrape surfaces or materials. A blade may be made from a flaking stone, such as flint, metal (usually steel), ceramic, or other material. Blades are one of humanity's oldest tools, and continue to be used for combat, food preparation, and other purposes.

Uses

During food preparation, knives are mainly used for slicing, chopping, and piercing.

In combat, a blade may be used to slash or puncture, and may also be thrown or otherwise propelled. The function is to sever a nerve, muscle or tendon fibers, or blood vessel to disable or kill the adversary. Severing a major blood vessel typically leads to death due to exsanguination. Shrapnel wounds via the fragments' blade-like nature.

Blades may be used to scrape, moving the blade sideways across a surface, as in an ink eraser, rather than along or through a surface.

Physics

A simple blade intended for cutting has two faces that meet at an edge. Ideally this edge would have no roundness but in practice all edges can be seen to be rounded to some degree under magnification either optically or with an electron microscope. Force is applied to the blade, either from the handle or pressing on the back of the blade. The handle or back of the blade has a large area compared to the fine edge. This concentration of applied force onto the small edge area increases the pressure exerted by the edge. It is this high pressure that allows a blade to cut through a material by breaking the bonds between the molecules/crystals/fibres/etc. in the material. This necessitates the blade being strong enough to resist breaking before the other material gives way.

No symbol

The no symbol (also known as a prohibition sign, no sign, circle-backslash symbol, nay, interdictory circle, or universal no) is a circle with a diagonal line through it (running from top left to bottom right), surrounding a pictogram used to indicate something is not permitted. The no symbol is generally colored red, but is sometimes another color, typically black.

The Unicode code point for the prohibition sign (also called the no symbol) is U+20E0;, Combining Enclosing Circle Backslash (   ⃠   ). It is a combining character, which means that it appears on top of the character before it, so putting d⃠ will show   d⃠.   (Note: This will appear only if the character exists in an available font.) It also appears in the Webdings and Wingdings 2 fonts.

There is also a prohibition sign emoji located at U+1F6AB NO ENTRY SIGN (🚫), which does not combine with anything.

According to the ISO standard (and also under a UK Statutory Instrument), the red area must take up at least 35% of the total area of the sign within the outer circumference of the "prohibition sign". So 35% of everything within the outer edge of the "no symbol" must be the symbol itself. Additionally, for printed signs under the UK rules, the width of a "no symbol" is set at 80% the height of the area it is printed to.