Backpack
A backpack, also called knapsack, schoolbag, rucksack, pack, booksack, bookbag, haversack, packsack, or backsack, is in its simplest frameless form, a fabric sack carried on one’s back and secured with two straps that go over the shoulders, and is used to carry goods from one place to another. It can feature an external or internal frame to transfer heavy loads off the user’s shoulders and onto their hips, reducing strain and increasing comfort on long hikes with heavy gear.
Backpacks are commonly used by hikers and students. They are often preferred to handbags for carrying heavy loads or carrying any sort of equipment, because of the limited capacity to carry heavy weights for long periods of time with their hands.
Large backpacks, used to carry loads over, as well as smaller sports backpacks, usually offload the largest part of their weight onto padded hip belts, leaving the shoulder straps mainly for stabilizing the load. This improves the potential to carry heavy loads, as the hips are stronger than the shoulders. It also increases agility and balance, since the load rides closer to the wearer's own center of mass.
Terminology
The word backpack was first recorded in the United States in 1914. Moneybag and packsack were used prior, and now occur mainly as regionalisms.The word rucksack is a German loanword mainly used in the US, UK, and other Western countries by hikers and campers. In Middle High German ruck means "back", which led to the Upper German word ruggsack. In modern German the word "der Rucksack" is commonly used. The name rucksack is cognate with the Danish rygsæk, Norwegian ryggsekk, Dutch rugzak, Afrikaans rugsak, Swedish ryggsäck, and Russian рюкзак.
The word knapsack was the usual name for a rucksack or backpack up until the middle of the 20th century.
Alternative names include haversack from the German Hafersack meaning "oat sack", Kraxe, and bergen.
Designs
Backpacks in general fall into one of four categories: frameless, external frame, internal frame, and bodypack. A pack frame, when present, serves to support the pack and distribute the weight of its contents across the body more appropriately, by transferring much of the weight to the hips and legs. Most of the weight is therefore taken off the shoulders, reducing the chance of injury from shoulder strap pressure, as well as being less restrictive of the upper body range of motion. Most backpacks can be closed with either a buckle mechanism, a zipper, or a dry-bag type closure, though a few models use a drawstring fitted with a cord lock for the main compartment.A bodypack is a backpack fitted with one or more pockets that are suspended on the wearer's chest and loaded in such a way that the load in the front and the load in the back are close to equal. The majority of the load in a bodypack is carried by the hips. The ideal load-carrying system should not disturb the wearer's natural posture, balance, and maneuverability. The load must be dispersed onto the skeletal structure in an even manner and should not produce unbalanced forces on the body.
Frameless
The simplest backpack design is a bag attached to a set of shoulder straps. Such packs are used for the general transportation of goods and have variable capacity. The simplest designs consist of one main pocket. This may be combined with webbing or cordage straps, while more sophisticated models add extra pockets, waist straps, chest straps, padded shoulder straps, padded backs, and sometimes reflective materials for added safety at night. These packs are generally produced inexpensively.Some outdoor packs, particularly those sold for day hikes, ultralight backpacking and mountaineering are sometimes frameless as well.
Sports
Sports and hydration backpacks are smaller with a profile closer to the body, wider straps, and can come with water bladders and hip belts for running, cycling, or hiking. Running hydration packs are the smallest and lightest, many under and most under. Compression straps across the top of one's body are common, as are hip belts. Cycling hydration packs are sitting high on the back. Although daypacks are small, averaging, all trekking and hiking hydration packs are generally the largest and heaviest. and above are common.External frame packs
External frame packs were designed to carry heavy loads above, giving the wearer more support and protection and better weight distribution than a simple, frameless strapped bag. Wooden pack frames were used for centuries around the world. Ötzi the Iceman may have used one in Copper Age Alpine Italy, though some archaeologists believe the frame found with the body was part of a snowshoe. Such packs are common in military and mountaineering applications; metal versions first appeared in the late-19th century.The first external frame rucksack to receive a patent was made by Henry Clay Merriam, a U.S. Army officer during the late 19th century. Introduced in 1887, Merriam's innovative pack was made with drab duck canvas, which was attached to a light steel frame. In addition to two shoulder straps, the pack featured several leather straps that allowed the infantryman to attach his bedroll and canteen to the frame, instead of having them rest on his chest and hips. The most important feature, however, was the two hardwood rods that extended from the sides of the pack to leather pockets on a half-belt, which rested across the lower back and hips. This system allowed the pack to elevate off the back and shoulders, and thus transfer the weight of the load onto the hips. Though he tried in vain to sell his invention to the U.S. Army, he was only able to sell a few thousand packs to the New York National Guard, and the French and Austrian Armies.
Backpack design took another major leap forward with the introduction of the first aluminum external-frame backpack by Jack Abert, an avid hiker from Phoenix, Arizona. As a Boy Scout camp counselor, Abert saw firsthand how inadequate the backpacks scouts were using at that time, and set out to design a more comfortable pack. In 1947, he designed a contoured aluminum frame that was both strong and light, and shifted much of the weight off the shoulders and onto the hips. By 1950, his invention had received official approval from the National Council of the Boy Scouts of America, and by 1967, he had become the largest manufacturer of backpacking frames in the world.
Today's external frames are typically made from aluminum, other lightweight metal alloys, and recently reinforced synthetic polymers or plastic and are equipped with a system of straps and tautly-stretched netting which prevents contact between the metal frame and the user's back. In addition to comfort, this "stand-off" provides the additional benefit of creating air circulation between the frame and the wearer's back. For this reason, external frame packs are generally considered to be a "cooler load" than internal frame designs. External frame packs have a fabric "sack" portion which is usually smaller than that of internal frame packs, but have exposed frame portions above and below the sack to accommodate attachment of larger items. In addition, the sack can often be removed entirely, permitting the user to customize the configuration of their load, or to transport a non-conventional load such as a quartered game animal. Military packs are often external frame designs due to their ability to carry loads of different shapes, sizes, and weights.
A recently proposed type of external frame would be made from composite plastic, which is not flexible like current backpack straps are, and can be shaped like human spine curvature. In this type of backpack, the load would directly transfer to the shoulders through the non-flexible straps, which is helpful in preventing damage from long-term backpack carrying. This non-flexible structure also diminishes the momentum at the lumbar region of the back. The strap curvature would be shaped closely to normal spine curvature, with two flexible drawstrings to minimize backpack movement along the transverse plane. The straps of this backpack would be wide enough to distribute the pressure on the shoulders, with an internal white glass wool layer to absorb dynamic forces from movement. This backpack type is experimental, needing further development before usage.