A hand clap is a short event that causes a single pressure wave that quickly dies out. The image above shows the waveform for a typical hand clap. In the waveform, the horizontal axis represents time, and the vertical axis is for pressure. The initial high pressure is followed by low pressure, but the oscillation quickly dies out.
The other common type of sound wave is a periodic wave. When you ring a bell, after the initial strike (which is a little like a hand clap), the sound comes from the vibration of the bell. While the bell is still ringing, it vibrates at a particular frequency, depending on the size and shape of the bell, and this causes the nearby air to vibrate with the same frequency. This causes pressure waves of air to travel outwards from the bell, again at the speed of sound. Pressure waves from continuous vibration look more like this:
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Judo is a combat sport involving close bodily contact so discipline and hygiene are important considerations. The judogi should be washed after every training session, the finger-nails and toe-nails should be clipped regularly and kept short to prevent the risk of injury and feet should be kept clean and, if necessary, washed before practice. A pair of zori, or slippers, or flip-flops should be worn when walking from the changing rooms to the dojo to avoid transferring dirt and germs to the mat. If hair is long it should be tied back and female competitors must wear a T-shirt under the judogi. All jewellery, chains, rings and such like must be removed before practising.
In randori the prohibited actions should be clearly understood. Kicking, punching, hair-pulling, biting or indeed any action likely to cause injury to an opponent are all unacceptable on a judo mat. Foul language and displays of bad temper are also unacceptable. Judo has an excellent reputation for sportsmanship and continues to fulfil Kano’s ideal of mutual respect and mutual benefit in a competitive framework.The motto of Gunji Koizumi, who founded the Budokwai in 1918, was ‘In skill opposed, in spirit united’, which expresses the ideal rather succinctly. Practice fighting should never become personal. There is nothing wrong with fighting spirit and aggression in a judo context, but it must be tempered with control and care for training partners. Of course, sometimes accidents happen or less skilful players prove to be clumsy, heads clash, shins are kicked when a foot sweep is mistimed, but such mishaps ought never to become an excuse for bullying. Anger has to be controlled. The hot-headed individual is his own worst enemy and can generally be easily provoked by a cunning opponent into making the kind of mistakes that can lose a contest.
The sensei, judo teacher or instructor, has the job of making sure these things are communicated to and understood by all beginners and new members of a judo club. Higher grades should guide and look after lower grades and all grades should behave in a mutually respectful way. Where beginners are concerned it is helpful for the sensei or instructor to have a few experienced players on the mat to help disseminate the information and teach these principles by example.
One of the procedures which helps to provide a framework of courtesy and discipline in which to train is the bow or salutation. Before and after each practice and each time they change partners within a practice players bow to one another. The bow or rei is also used to begin and end actual contests. This simple act is of immense value, since it allows both players to show mutual respect and appreciation for one another and clearly defines the beginning and the end of the combat situation.
On the mat the sensei’s word is law. It is truly important that there are senseis in judo and that they receive the respect they deserve. Particularly at area or national squad level, the players must not be allowed to run the mat. They do not as a rule have the maturity, the experience or the objectivity necessary to do so. Individuals’ perceptions of their strengths, weaknesses, abilities and needs are quite often far from accurate; the sensei, who will inevitably have many years of experience, is a much better judge of what they really