Things as simple as a knife can also be classified as a simple machine, specifically, a wedge. A knife is a cutting tool, composed of a blade and a handle. A wedge is basically an inclined plane, that can be used to penetrate or split objects, or to stop them from moving, and reduces the force needed to cut through those objects. When the knife is used for food preparation, the main uses are slicing (which involves cutting, by drawing the blade across the food, applying light pressure). Since the knife was among mankind's earliest inventions, the answers to who invented it, and what time it may have been invented may not be accurate, and varies among different sources. However, it is believed that it was first used by the cavemen during prehistoric times, who made crude knives from pieces of obsidian.
The knife can be used in many different ways, mostly depending on the type of knife that is being used, whether the knife is being used as a weapon, as utensils, as tools, or as a traditional or religious implement. The tool itself does nothing, but in the hand of the user it transmits the pressure of the hand and the arm. Knives concentrate a large amount of force on a very small area. The pressure from the arm down upon the sharpened edge, driving it into (for example), a tomato. The force between the food and the knife is normal force (the force of a surface acting on an object). When the right amount of force is applied, the knife overcomes the normal force of the food and cuts through.
The blades of a knife nowadays can be manufactured from a variety of materials, ranging from flint to steels, to stainless steel, to aluminum alloy, cobalt alloy, molybdenum, titanium, tungsten, chromium and other assorted metals with a relatively high melting point. In the old days, knives used to be made of stone and other materials as technology back then was not as advanced when compared to today. Knives nowadays are better, and are more durable as they use stronger metals and sharper edges. Unlike knives in the olden days, which blades made of stone were too rough and coast, and could only chop and not cut. This meant that foods and another things could not be cut at a precise angle or shape. Today, with a more defined blade, foods like sashimi can be cut at a more precise angle, therefore creating a different dimension of taste and texture to the fish.
In most cases, knives are effective to its cause, as mentioned above, although there are also side effects to it, regardless of what material for the blade is being used. Using a blunt knife to cut things with is extremely dangerous, and is considered to the the most common side effect to this tool, as they require more pressure to cut. This increased pressure and the inability of the knife to cut into the object increases the likelihood of the knife slipping, therefore cutting a finger or perhaps stabbing a hand. Also, some knives (ceramic knives in particular) require high abilities to sharpen as they are dangerous, and therefore can only be done by professionals. They can also cause damage to dinnerware cause of their...