The folk implement shown below, which can still be seen in operation in some museums by way of a demonstration, carries out the function of threshing rice by converting the reciprocating motion of human power into a rotating motion.下の民具は，現在でも資料館などでは稼働するものもあるが，人力による往復運動を回転運動に変換し，その回転により稲穂の脱穀の機能を具現化する。
A rotating mill Dozurusu made of clay and a lever yariki to drive it
このT字形のものは「やり木」と呼ばれのもので，下の絵図のように天井からロープで吊り下げ，複数名で押し引きの前後への往復運動を行い，それを円筒状の脱穀装置「土摺臼」を回転させる。
The T-shaped lever is called a yariki in Japanese, and it is suspended from the ceiling by a rope as shown in the left part of the old picture below, where several people seem to be on the verge of pulling and pushing it back and forth to rotate the cylindrical threshing machine, or dozurusu.
下の絵の様子では，今，土摺臼の上に籾を補給し，これから歌いながらでもやり木に振り子運動をさせようと待機しているのであろう。土摺臼の右下には，この方式の一つ先輩である木摺臼による脱穀が進行中である。こちらは「半回転」と呼ばれる，回転方向の異なる回転運動の繰り返しとなっている。
In the picture below , the four people on the left who seem to be chatting to each other are probably waiting for the dozurusu to be filled with unthreshed rice, and to make the T-type pendulum move while singing. To the lower right of the dozurusu, a threshing operation is in progress using a wooden mortar kizurusu, which is historically older than the dozurusu. This threshing method is called “semi-rotation”, which means that the kizurusu rotates periodically changing direction (clockwise or counterclockwise). The threshing method of the dozurusu is different and more effective for carrying out this work and the direction of its rotation tends to be unidirectional.
出典：堀家本四季農耕絵巻一巻より Pictorial representation of a farming scene in the Edo period
Trajectory of a 2D model with two springs replacing the ropes at the both ends of the yariki
この図は天井からのロープを左側黄緑の２本のバネに置き換えたものである。T型のやり木のハンドル部（左側の軌跡）から，このロープがあることで，やり木の自然な左右方向への前後運動が，右側の臼をモデル化したリンクに一方向の回転運動を与えていることが理解できる。
In this figure , the rope from the ceiling is replaced by two yellowish-green springs on the left side, and it can be understood from the trajectory of the yariki (left-hand trajectory) that the natural back and forth motion of the yariki in the left and right directions, due to the presence of this rope, gives a stable unidirectional rotational motion (counterclockwise) to the links modelled as the dozurusu in the middle of the picture.
Trajectory of a 2D model without the two springs
試みに，このロープによる支えがない状態で，やり木を同様に動かそうとすると。本質的に大きく左右上下にぶれてしまうことが予想され，絵図に見る天井からのロープの役割の大きさに感心することになる。ここにも単純な物理現象を利用した仕事の効率化，無駄のなさのが見られて興味深い。
If one were to try to move the ladder in the same way, without this rope support or the two springs, it would predictably move unstably left to right, right to left, up and down, and we would be impressed by the great role played by the rope from the ceiling. It is interesting to note here the efficiency of work and avoidance of wastefulness achieved by using simple physical phenomena.
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