skateboard; skateboarding

abstract

Skateboarding is the originator of the history of extreme sports, and many extreme sports are extended from skateboarding. Skateboarding originated from surfing in the late 1950s and early 1960s, and now it has become the coolest sport on earth. The skills of skateboarding mainly include: air (on the sliding bar), inversion (on the U-shaped platform) and Ollie (taking off with a board). These skills can be said to be the most important skateboarding action besides turning over. Two important international skateboarding organizations in the world: International Association of Skateboarding Companies (IASC)J and World Cup Skateboarding (WCS).

The history of skateboarding

On the other side of the Pacific Ocean in the late 1950s, Edison's descendants, who were good at invention and creation, more or less turned the fantasy of ancient people in China into reality. In the early 1950s, the west coast of the United States was a place where trendsetters tried their best. They use surfboards made of ordinary wood and expensive balsa wood to have fun on the cusp. By the mid-1950s, molded polyurethane foam and glass fiber had replaced wooden surfboards. The mobility and durability of these new surfboards made surfing very popular in the late 1950s.

Skateboarding is an extension of land surfing. The former is limited by geographical and climatic conditions, while the latter has greater freedom. Residents of the Sunshine Beach community in Southern California soon made the world's first skateboard.

Today, this is a rather primitive invention: a 50*50CM board is fixed on the iron wheel of roller skating. Even such a simple exercise device has aroused people's interest because it can provide the same psychological feeling brought by surfing.

However, due to its backwardness (the board is too heavy and inflexible, the steering mechanism is not sensitive, and the wheels are too slippery, etc.). ), skateboarding has not been so popular today. This earliest skateboard can be seen in the skateboard video program Ban This.

The second generation skateboard was born in 1962. This is composed of 15 * 60cm oak laminated board, roller-skating steering bridge and plastic wheels. Compared with the first generation skateboard, this kind of skateboard is undoubtedly a technological leap. However, the performance of the plastic wheel of this skateboard is still very unsatisfactory. His adhesion friction is too small, which makes the skateboard out of control when turning sharply; His low elasticity means that the skateboard will suddenly stop when it meets even a small obstacle, and the skater will fall off. At the same time, his wear resistance is too poor. Nevertheless, this kind of skateboard is still popular with skaters. After all, skateboarding has evolved to a great extent compared with the previous generation, and the relatively wide board surface makes it easier for skaters to stand and control. Most skateboards sold in China now belong to this second-generation product.

1973, a skateboarder named Frank Nasworthy installed polyurethane wheels on his skateboard for the first time, and achieved unexpected results. He immediately began to sell the wheel called Cadillac to his skateboarding friends. This flexible wheel is not only wear-resistant, but also allows the skateboard to turn safely and smoothly and easily run over small obstacles on the ground. This is how the third generation skateboard was invented. Because skateboarding originated from surfing, the skateboarding culture in the early 1970s was basically a culture with traces of surfing. Skateboarding enthusiasts and the builders of skateboarding parks initially built many terrains to simulate surfing. Later, they finally realized that because skateboarding has less resistance and lighter weight than surfboards, they can build terrain that is different from surfing and more suitable for skateboarding to achieve greater speed, mobility and self-expression ability.

The "West Wind" skateboarding team in Santa Monica, California, USA, used the abandoned keyhole swimming pool as a venue for practicing vertical water skateboarding, which formed a swimming pool search fever in California for a time. Since then, skateboarding and surfing have become a prominent force, not only from equipment, venues, but also from personnel. Instead of surfing, this new army devoted itself to skateboarding and began to form its own language, skills, clothing style and music hobbies. Formed a new, city-oriented skateboarding secondary culture.

The mid-1970s was a period of rapid development of the third generation skateboard. It is predicted that a new type of sports will emerge as the times require, and countless small skateboarding companies established by skateboarders and surfers have sprung up like mushrooms after rain and started to compete in technical quality. The potential of polyurethane wheels is fully tapped. The continuously improved polyurethane wheels enhance the adhesion friction of the skateboard, improve the speed and even slide on the vertical plane.

In addition, the research and development of skateboard materials has reached the end of the road. Hard plastics, aluminum alloys, glass fibers, and even high-tech carbon composites are used to trial-produce skateboards. Finally, Canada Sugar Maple, which has good impact resistance and light weight, has undertaken the historical mission of a new generation of skateboard materials.

In addition, the polyurethane wheel invented by Powell Company and the concave skateboard tail patented by Stevenson became the third generation skateboard after going up a flight of stairs.

At the end of 1980s, due to the development of skateboarding itself and the improvement of skaters' technical requirements for skateboarding, and in order to meet the needs of two-way sliding of U-shaped pool, a kind of skateboard with inclined ends and symmetrical shape appeared, which is the fourth generation skateboard. Currently, only skaters use the fourth skateboard. The fourth generation skateboard is changed to hard stone maple, which is lighter and more elastic. Skateboard wheel has high hardness and good elasticity, which is more suitable for high-speed sliding. Because of the balance of weight, the fourth generation skateboard is more suitable for all kinds of flip movements.

In the early 1990 s, skateboarding entered a trough. Because it is in the period of skateboarding renewal, skateboarding has changed from one end to two ends, so there are many actions that the previous generation skateboarding can't complete. This period is the era of skateboarding skills. The skater invented many new moves. At the same time, in order to make the skateboard turn over more easily, the skateboard surface becomes very narrow and the wheels become very small. The typical skateboard in this period is only 7 inches wide, and the wheel diameter is only about 39 mm. Although such a skateboard is easier to make complex movements, the smaller wheels hinder its sliding performance.

Sliding plate culture

With the development of skateboarding, skateboarding technology is catching up with its ancestors surfing. Allen Gelfand invented Ollie, which made skateboarding pay more attention to high-tech performance and produced many stars such as Tony Hawk and Steven cavallero. Touring brand promotion activities organized by skateboarders and famous companies have brought great benefits to businesses and have become a common method of industrial marketing. Skaters' earth clothes and nostalgic sneakers once became the world trend, and the related music (new wave music, punk, hipop) also reached its peak. Its language, skills, costumes and music constitute a unique skateboarding culture. There are as many as 4.5 million skateboarders in America! Skateboarding is too exciting In the 1960s, skateboarding was strictly prohibited by the government and once became an "underground project". It was not until the mid-1980s that the skateboarding project was publicly lifted by the government, which made this urban magic sport make a comeback. Skateboarding superstars Tony Hawk and Andy McDonald are undoubtedly the same super idols as Jordan and Sampras in the eyes of many young people.

Types of skateboards

1. Entertainment type

Recreational skateboarding is used for beginners' fitness. Beginners should choose a flat skating rink and wear elbow pads, wrist pads, knee pads, helmets and other protective gear when skating.

sports

Sports skateboarding is suitable for skateboarders with high skating skills. Because athletes have to do all kinds of difficult movements and patterns, the strength and performance indexes of all parts of the sports skateboard should meet the requirements of use.

Second, the structure of the skateboard

The skateboard is mainly composed of bracket, buffer sleeve, wheel, lock nut, buffer pad, bracket seat, pedal and so on.

Third, performance indicators.

1. Wheel:

When selecting materials, we should consider that they are suitable for different site pavements, such as floor pavements, cement pavements and asphalt pavements. No matter what road surface you slide on, the wheels must have good elasticity, wear resistance and moderate hardness, and also ensure that the wheels have sufficient friction coefficient on the road surface.

2. Cushion pad and sleeve:

It mainly plays the role of cushioning and shock absorption. One is to play a damping role when the road surface is uneven; The second is to protect the parts when the amount of exercise is large; The third is to keep your body balanced.

3. Pedal:

It is made of high-grade wood multi-layer boards glued together. It has high strength, impact toughness and good elasticity. When jumping on a skateboard with a certain height, ensure that the pedal is not damaged.

Fourth, safety precautions

1. Adjust the wheels before use to make them run freely.

2. Adjust the elasticity of the cushion reasonably with the lock nut according to your own usage.

3. Oil the bearing regularly to increase the lubrication of the bearing and reduce the sliding resistance.

4. Beginners need to slide on the slope with small inclination with the help of relatives and friends, and gradually change different slopes with the improvement of technical level.

5. Don't slide on wet or uneven roads. When you want to jump off the skateboard, see if you can bump into people or other things around you.

6. If it is necessary to replace parts, the replacement parts shall have the same specifications and models as the original parts.

Skateboard parts

It is very important to choose the right equipment for skateboarding. Skateboarding is made up of several different parts. Due to the different terrain and mode of skateboard, the parts are also different. Generally speaking, skateboarding consists of the following parts:

1.deck, 1, generally made of five-layer, seven-layer and nine-layer maple boards by microwave cold pressing. There are also panels made of aluminum alloy, carbon fiber and other materials. At present, the board face, the board head and the board tail are all inclined. Personally, my favorite plate type is 20cm*8 1cm, with a slightly round head. The board surface above 22cm can basically be regarded as the board surface of U pool, and its board can accommodate more feet and is more stable on U pool. 19cm boards are mostly used for flat road conditions. The sub-plate can move flexibly and quickly after being equipped with small wheels. In addition, different companies have different depths of slabs and footpits. Some skaters like the board with deep footwell, which makes it easier to make the action related to turning the board and is more stable when doing Ollie.

2.griptape (1 sheet) is attached to the upper surface of the board to increase the friction with the sole and facilitate the control of the skateboard.

3. Trucks, two in number, are metal parts, fixed under boards, and wheels are mounted on bridges. The bridge allows children to turn, and can adjust its turning speed and angle.

Bridges play an important role in the performance of skateboards. At present, most of the bridges produced in the United States are special aluminum alloys, and almost no longer break. Spans of skateboard bridges are 126 mm, 129 mm, 134 mm, 139 mm, 146 mm, etc. Skateboarding bridges with different spans and boards with different widths make skateboarding more flexible and easier to control. The height of the bridge is also different. The higher bridge is suitable for installing larger wheels, and the lower bridge is suitable for installing smaller wheels, so it will be more comfortable to slide, and it is unlikely that the wheels will hit the board when bending or the main bridge nail will break due to excessive bending.

INDY, VENTURE, DESTRUCTO, Thunder, Orion, GRINDKING, TITAN (Nissan) and other bridges are all good. Indy is known as the king of bridges, and its quality is self-evident. There are also quite a few people using VENTURE in America. DESTRUCTO is the best-selling bridge in America and my personal favorite bridge. DESTRUCTO is very smooth when doing the action of sliding bridge on the round bar (such as 50/50, 5/0, K-GRIND, etc. ), and it is very stable. Orion's PU cushion is so good that it can be as hard as a stone when twisted, and it won't explode no matter how you use it. GRINDKING's bridge is the lightest, but the steel bar in its central axis is not very hard, it will bend if it jumps too much, and it is not wear-resistant, but its main bridge nail is quite good, and it is reverse. Titan, according to friends who have seen it, is very good, beautiful, lightweight and rust-proof, but it is a little more expensive than ordinary bridges.

4. Four skateboard wheels made of polyurethane. Wheels come in different diameters, shapes and hardness. The small boat starts fast, but it lacks stamina and is suitable for skills; Big wheels are easier to slide on uneven ground.

Skateboard wheels also have a lot to say. Except the accuracy of bearings (such as ABEC 1, ABEC3, ABEC5, ABEC7, etc.). ), it depends on the performance of the wheel.

The first is hardness. Skateboard wheels are usually made of polyurethane, and the hardness of the wheels varies with the proportion of polyurethane in the wheels. Wheels with hardness of 85A(A stands for hardness) are soft, suitable for sliding on rugged roads, and the sound is extremely low when sliding, which is a good choice for friends who like to pedal shopping. However, the wheel of 85A is soft and not wear-resistant, and it is easy to break the spacer when doing sideslip braking and other actions. Nowadays, skaters generally use 97A- 103A wheels. This kind of hard wheel is suitable for smooth marble and flat road surface, as well as props such as U pool and platform jumping. There is no sound in smooth and flat places, such as the wheels of 85A. But in rugged places and on the U-shaped pool, there will be a loud rumble (this kind of sound often makes the wrench have a boiling blood). 103A is used for transparent or translucent wheels. It's too hard and will crack. It is best to use it only on props made of all wood materials.

The second is the diameter, and now 38-40mm wheels are rarely used. This kind of wheel starts quickly and accelerates quickly, but its stamina is small. It is only suitable for very flat roads, and its characteristic is quite flexible. Friends who like small moves can try. 45mm-50mm wheels are the most suitable wheels for road types. 52-60mm wheels are more suitable for props. Because the action on the props needs strong power, the flat action wants the board to be as light as possible, and the heavy board on the props can sometimes bring greater inertia and impact, allowing you to fly higher and farther. You can choose cross-country wheels over 60 mm in the field, and professional mountain skateboarding uses large rubber wheels.

There is also a rebound, and the rebound of the wheels is very important. Although there are no parameters to refer to. However, the stronger the rebound, the stronger the ability to overcome obstacles. If you don't know how well your wheels bounce, you can do a small experiment. Remove the bearing from the wheel and throw the wheel to the ground. If the bullet is high, the wheel will bounce to the ceiling, and the wheel that bounces at the bottom will only bounce to the ground twice. On the flat ground, perhaps, the two kinds of wheels run as fast, but when encountering uneven road conditions, the advantages of high rebound wheels will immediately appear.

5. There are 8 bearings, and each wheel is equipped with 2 precision bearings. Bearings have different precision and durability. Generally speaking, bearings have an ABEC mark, ranging from ABEC- 1 (the least accurate) to ABEC-7 (the most accurate). However, some bearings do not have the symbol of ABEC. For example, bone bearings have never had the ABEC logo, but their bone Swiss ceramics are one of the best skateboard bearings.

Skateboard flat noodles

The board surface is the most important part of skateboarding. The choice of board surface has a great influence on the performance of your skateboard. So what kind of board is the best? It depends on your needs. Do you need Ollie to be tall? Or is it better to be taxied? Or the most durable? Now let's look at several different criteria for choosing skateboards.

The shape of the skateboard. This is the most commonly used criterion for choosing skateboards. When choosing a shape, you need to pay attention to many factors. Length, width, plate head length, plate tail length, bridge distance. Now most skateboards are between 7.5 inches and 8 inches wide. Some of them are narrower or wider, but most are less than half an inch apart. It is best to be familiar with the unit of "inch", because the boards on the market and online are all inches, and it is very troublesome to convert them into centimeters.

There are other aspects to pay attention to when choosing a skateboard. If your board is broken and cracked, you need to replace it with a new one. If the tail brake is used frequently, the edge of the tail will become sharp, which is the so-called "razortail", so that the tail will easily break into small pieces, thus reducing the elasticity of the board. Water and cracks will also reduce the elasticity of the plate. All these factors will affect the elasticity (or length, if you like) of the board.

As far as durability is concerned, no board has an absolute advantage. Most of the board faces are 7-layer boards, which are bonded together with 7-layer thin plates. Some companies claim that their boards are very light, and most of them use thinner boards, or fewer layers, or cross plywood. These methods make your board a little lighter, but also make it a little weaker. Some companies even add more layers or enlarge the footwell of the board to increase its durability.

Some companies have adopted different practices or innovations in the board structure. For example, the patented technology of "new wave structure" of Flip Company adds a layer of corrugated hard strips on the surface of the plate to improve the performance of the plate. Real company adopted the "triple beam structure", and used seven layers of plywood, three of which were cross-glued. This greatly increases the flexibility and durability of the board.

If your board is hard, you can give full play to its performance. If it is spongy (caused by water or excessive distortion), then its performance is not good. But if it is too hard, it will become fragile. And then there's an intermediate value, right? Skateboarding companies are innovating every day, trying to make themselves masters of skateboarding manufacturing technology. But we still haven't found a better way.

I need to remind you that no matter how bad your board is, too thick, too thin, too soft, too brittle, and the slag falls off badly, the problem with your skateboard is probably your own. Don't forget the fun of skateboarding!

Selection of skateboard bridge

Skateboarding bridge, with wheels on it, is the most durable part of your skateboard. You can use it to grind all kinds of surfaces. They can transform you. Now you know they are very important. Let's take a look at the composition of the bridge: it consists of the shaft sleeve/shaft, the main nail of the bridge, the bushing and the bottom plate.

The base plate is the part fixed on the board surface. The thick screw passing through the bottom plate is called the kingpin. You can adjust the tightness of the pivot pin to control the flexibility of the bridge. The main nail is the most easily damaged part of the whole bridge, but it can be replaced. Bushing is above the main nail, and each bridge has two bushings, one large and one small, with different hardness. With your use and abuse, they will break, and then your bridge can't be tightened. Fortunately, many bridge manufacturers offer replacement sleeves with different hardness.

One of the problems of bridges is "axis sliding", when the board hits the ground with its side and its axis is perpendicular to the ground (the term is primo). The shaft slides in the shaft sleeve so that one wheel is tight and the other wheel is loose. The general way to deal with this situation is to primo the board in the opposite direction, but it is conceivable that the problem of sliding shaft will only get worse after a long time. Many companies claim that their bridges are "anti-skid". You can have a try.

Don't listen to others say whether the bridge is tight or loose. It all depends on your preference. A loose bridge is easy to turn, but a tight bridge is more stable. You can also tighten the rear axle slightly, so Ollie is more stable.

Of course, another aspect of choosing a bridge is weight. Nobody wants a heavy bridge ... hey, does anyone want it? ..... I hope not, hehe. Some companies try their best to reduce the weight of bridges while maintaining their strength. Mill king and thunder are relatively light, while independence and destroyer are relatively heavy.

Bridges have different widths. A bridge too wide is installed on your board and looks like a turtle. When you turn the chessboard, the bridge will touch your feet. The narrow bridge prevents you from seeing the wheels when you slide. One principle of choosing the width is to erect the side of the plate after the bridge is installed, so that it can be placed basically vertically on the ground. So you can do something like somersault.

Wheels are a neglected part of your skateboard, but wheels determine how you feel when you skate. It depends on where you skate-street, U-pool, swimming pool or indoor cricket field-which will determine what kind of wheels you choose (including size and hardness). When you face all kinds of wheels in a skateboard shop, you will drool. You may think that they just look different and use the same, but you are wrong.

When selecting wheels, color and pattern may be important factors, but function is more important. If you want to choose the best set of wheels, there are several keys: no wheel can fit all the ground (you will think, oh, do you want me to bring several sets of wheels and change them at any time? If you skate on the same ground most of the time, you don't have to worry. You can refer to the following instructions or consult an experienced skater to make the best choice.

Wheels are made of polyurethane, which is a chemically synthesized hard rubber. Improve the performance of wheels by changing the proportion of chemical components. Every company has its own formula, so you will feel a little different when you use it. The ideal wheel you are looking for must have good elasticity, certain hardness, high speed and durability. Famous companies try to do this by changing different formulas.

When you get a set of wheels, you need to pay attention to two factors: hardness and size. Hardness (10 1A) is the hardest grade in a wheel. Most wheels have only one hardness, but there are also two hardness. Usually, the inner layer or interior of a wheel is made of hard material, and the outer layer or exterior is made of soft material.

The dimensions of wheels are recorded in millimeters (for example, 55 millimeters). Generally speaking, the bigger the wheel, the faster the speed, but the weight will naturally increase. The wheel also has a width value, which we seldom mention. Regardless of the wheel weight, the wider the grip, the better. Of course, the wheels should match your board, and the smaller board should match the smaller wheels.

difficulty

87A- Very rough ground (steep slope, etc.). )

95A- Rough ground (block)

99A- Smooth floor (various markets, skatepark, U-shaped pool, swimming pool)

10 1A- Not suitable for rough or very smooth ground (poor grip because it is too hard).

size

52-55mm- Suitable for most users. Market, skateboard park. Little skater.

56-60mm- Suitable for most users. Market, skateboard park. Adult skater.

60+mm- special skater. Lengthening the board, downhill, mud.

Beginners had better choose wheels with lower hardness, because they can't drive skateboards well to avoid pebbles, glass and debris on the road. If the hardness is too high, these fragments will jam their wheels, while experienced skaters usually choose harder wheels.

If you are a beginner, you'd better consult your friends or try several wheels with different hardness and size to help you make a decision.

Safety of skateboarding

Skateboarding is a safer sport. The following is a comparison table of 1997 American sports injuries. It can be seen that the proportion of skateboarding injuries to the total number of people is very low compared with other sports, even after fishing!

1997 American injuries for each selected activity

total participants * | total njuid | Treated & amp； Discharge (%) | Hospitalization (%)

Each participant

Ice hockey 3 18000 77492 98.9 0.9. 244

Baseball 2033000 326569 98.21.1.161

Basketball 4.527 million 64492 199 0.6. 142

soccer

Football 282500014891398.31.1.053

Golf 97 1 0,000 39,473 95.6 2.3.040

Snowboarding 1, 037,000 37,638 96.7 2.5.036

Volleyball 2.732 million 67340 99.4 0.5. 025

Fishing 3812000 72598 98.8 0.819

Skateboard 8.238 million 48 186 95.2 3.9. 006

This may be because skateboarders usually wear various protective equipment, such as helmets, knee pads, elbow pads, palm pads and so on. Skateboarders who usually exercise on various U pools need to wear these equipment. Because these devices hinder sports, and street skateboarding is slow and has little influence, many street skateboarders don't wear these, but it is recommended to wear helmets at least.

The other side of security comes from yourself. Don't do actions beyond your ability, and don't do more difficult actions in unfamiliar places. Before doing all kinds of skills, check the terrain and see if there are any dangerous things nearby, such as broken glass and sharp fence tops. Don't carry sharp objects with you.

Skateboarding Guide With the popularity of extreme sports, more and more young people join the so-called extreme skateboarding. Because skateboarding is ornamental and easy to learn, many fans are eager to try it. The first thing to do is to choose the board. Skateboard is generally composed of board surface, skateboard bracket and skateboard wheel, which is also a high cost part. A good skateboard generally needs its own configuration. There are some accessories such as bearings, sandpaper, screws and other small items.

Skateboards and other equipment

1. Skateboard shoes:

The quality of skates is also very important for a good skater. Generally speaking, there are several points to pay attention to when choosing skateboarding shoes.

Strength of board shoes: the soles and uppers of skateboarding shoes should be made of polyurethane, and the uppers should be made of thick suede leather, which is more wear-resistant. Ollie should pay attention to the position of the shoes he usually uses when taking the board, and try to avoid the shoes with wiring in these positions when choosing shoes, so as to avoid the premature scrapping of the board shoes because of off-line. ※. Now the new shoes made by CONVERS are covered with "ABR" super wear-resistant materials, which are very durable.

Comfort of board shoes "For some skilled skaters, they prefer to use relatively thin board shoes. The soles of these shoes are thin, but they usually have thick insoles or insoles with air cushions. ※. The leather used for the vamp is soft, and you can obviously feel the sand on the board sticking to your feet when you do the action. However, more active skaters generally choose thicker skates. For example, the sole has an air cushion or an oil pad, and the tongue of the shoe is thicker, which makes it feel more foot-bound.

As for the brands of skateboarding shoes, there are too many. Among them, the best-selling DC and VANS have also supported skateboarding for many years, as well as Kastel, Deffs, DVS, Converss, 2 Fish, Bizo, Adio and so on.

2. Skateboarding clothes:

Skateboarding clothes are mainly loose, and most players choose skateboarding company T-shirts or HIPHOP-style clothes. Some people think skateboarding is counter-mainstream and needs to be weird. In fact, some skateboarding experts think that skateboarding is a real sport, and Tony Hawk (American skateboarding superstar) knows this very well, and gets tens of millions of dollars of industrial value from this sport every year. And he himself wants to be an ordinary track and field athlete.

3 backpack:

Skateboarding backpacks have many general functions. Skaters can consider a backpack of suitable size according to their personal situation. Generally, tools such as wrenches, simple spare parts such as clothes, spare tires and bearings are put in the bag. If it is big enough, put on a pair of shoes. Some skateboard bags are designed to tie the skateboard to the bag, which is more convenient to carry and will not increase the size of the bag. Red syrup and band-aid can also be put in small bags.

4. Protective equipment:

Skateboard protective gear includes helmet, knee pads, wrist pads (elbow pads), etc. Recommended for beginners or difficult movements. You need protective gear in general competitions.

Helmet: A good quality helmet is your most important safety device. If you don't wear a helmet when playing skateboard, you can recover quickly from bruises and sprains, but head injuries will greatly affect your future life. ※.

Knee pads: The most important invention of knee pads is the invention of plastic knee pads. The knee pads shown in the picture are all ideal, and many of them have good effects. It's better to wear any knee pads than not to wear them. ※.

Gloves: Skateboard gloves come in many shapes and sizes. In the United States and Japan, some people use motorcycle gloves as skateboard gloves, and some people use gardening gloves instead. The ideal glove is to fit your hand and protect it from injury when you fall. ※.

Wrist protector (elbow protector): Like knee protector, wrist protector with plastic brim is the best wrist protector, and there are many substitutes with the same function. ※.