Wobble board

The wobble board is a musical instrument invented and popularized by the Australian musician and artist Rolf Harris, and is featured in his best-known song "Tie Me Kangaroo Down, Sport". A wobble board, like some other musical instruments, can be ornately decorated because its large surface area can act as a canvas without detracting from its musical capability.

The instrument is played by holding the board lengthwise with the hands holding the edges and flicking the board outward, thereby making a characteristic "whoop-whoop" noise. The angle at which the board is held, and the way the board is "flicked", can alter the timbre of the sound produced. It is similar to the boards used to imitate the sound of thunder in the theatre of Shakespeare's time.

Official Rolf Harris wobble boards were sold commercially for a time in the 1970s but most are made by the player. Almost any large, springy and flexible sheet of material can be used as an impromptu wobble board, although some materials are markedly better than others. Harris's instrument was originally made from a type of wood composite known as hardboard (Masonite in the United States and Australia). According to an interview he gave to Tony Barrell for The Sunday Times Magazine in 2001, Harris discovered the musical properties of hardboard by chance in 1959, when he was about to paint a portrait of the conjurer Robert Harbin. Before his subject arrived, Harris prepared the background, covering a large piece of hardboard with Prussian blue oil paint mixed with turpentine. But the surface refused to dry. "It was all sticky and nasty. He was due to arrive in about half an hour." In desperation, Harris propped the board over a paraffin heater. When he touched it later, it was so hot it burned his finger. "So I propped it between the palms of my hands and shook it to cool it down. And ... I thought, 'What a marvellous sound.'"

Balance board

A balance board is a device used as a circus skill, for recreation, balance training, athletic training, brain development, therapy, musical training and other kinds of personal development.

It is a lever similar to a see-saw that the user usually stands on, usually with the left and right foot at opposite ends of the board. The user's body must stay balanced enough to keep the board's edges from touching the ground and to keep from falling off the board.

A different challenge is presented by each of the five basic types of balance boards and their subtypes. Some of them can be attempted successfully by three-year-olds and elderly people, and some, because of their steepness and speed, are difficult and dangerous for professional athletes.

In their design, what differentiates the five types (and their subtypes) is how unstable each of them is, i.e., in how many and in which of the three dimensions of space each board turns and/or sways and how freely its fulcrum contacts the board and the ground.