sonorous object hand, stick, striker or against a non-sonorous object human body, the ground. This is opposed to concussion, which refers to instruments with two or more complementary sonorous parts that strike against each other and other meanings. For example: 111.1 Concussion idiophones or clappers, played in pairs and beaten against each other, such as zills and clapsticks. 111.2 Percussion idiophones, includes many percussion instruments played with the hand or by a percussion mallet, such as the hang, gongs and the xylophone, but not drums and only some cymbals. 21 Struck drums, includes most types of drum, such as the timpani, snare drum, and tom-tom. 412.12 Percussion reeds, a class of wind instrument unrelated to percussion in the more common sense There are many instruments that have some claim to being percussion, but are classified otherwise: Keyboard instruments such as the celesta and piano. Stringed instruments played with beaters such as the hammered dulcimer. Unpitched whistles and similar instruments, such as the pea whistle and Acme siren. Percussion instruments are sometimes classified as pitched or unpitched. While valid, this classification is widely seen as inadequate. Rather, it may be more informative to describe percussion instruments in regards to one or more of the following four paradigms: By methods of sound production Many texts, including Teaching Percussion by Gary Cook of the University of Arizona, begin by studying the physical characteristics of instruments and the methods by which they can produce sound. This is perhaps the most scientifically pleasing assignment of nomenclature whereas the other paradigms are more dependent on historical or social circumstances. Based on observation and experimentation, one can determine how an instrument produces sound and then assign the instrument to one of the following four categories: Idiophone "Idiophones produce sounds through the vibration of their entire body." Examples of idiophones: Bells Bock-a-da-bock Cabasa Cajón Castanets Celesta Chimes Claves Cowbell Crash cymbals Crotales Daxophone Flexatone Glockenspiel Güiro Handbells Hi-hat Lummi stick Maraca Marimba Orchestra bells Quadrangularis Reversum Ratchet Singing bowls Slit drum Steelpan Suspended cymbal Temple blocks Thumb piano (or Kalimba) Triangle Txalaparta Vibraphone Vibraslap Wood block Xylophone Membranophone Most objects commonly known as drums are membranophones. Membranophones produce sound when the membrane or head is struck with a hand, mallet, stick, beater, or improvised tool. Examples of membranophones: Bass drum Bongos Conga Darbuka Djembe Mridangam Octoban Parai Rototom Snare drum Tabla Thavil Timpani Tom-tom Lion's roar Urumi (drum)