Oar
An oar is an implement used for water-borne propulsion. Oars have a flat blade at one end. Rowers grasp the oar at the other end. The difference between oars and paddles is that oars are used exclusively for rowing. In rowing the oar is connected to the vessel by means of a pivot point for the oar, either an oarlock, or a thole. The oar is placed in the pivot point with a short portion inside the vessel, and a much larger portion outside. The rower pulls on the short end of the oar, while the long end is in the water. By contrast, paddles, are held in both hands by the paddler, and are not attached to the vessel. Rowers generally face the stern of the vessel, reach towards the stern, and insert the blade of their oar in the water. As they lean back, towards the vessel's bow, the blade of their oars pivots in the oarlock, and the end in the water moves towards the stern, providing forward thrust. For thousands of years vessels were powered either by sails, or by the mechanical work of rowers, or by paddlers. Some ancient vessels were propelled by both oars and sail, depending on the speed and direction of the wind. Rowing oars have been used since the early Neolithic period. Wooden oars, with canoe-shaped pottery, dating from 5000–4500 BC have been discovered in a Hemudu culture site at Yuyao, Zhejiang, in modern China. In 1999, an oar measuring 63.4 cm (2 ft) in length, dating from 4000 BC, was unearthed in Ishikawa Prefecture, Japan. Oars have traditionally been made of wood. The form is a long shaft (or loom) with a flat blade on the end. Where the oar connects to the boat there is a "collar" (or button), often made of leather, which stops the oar slipping past the rowlock. Oars usually have a handle about 150mm long, which may be a material sleeve or alternatively an ovoid shape carved to fit the hands. Oars are levers. Which class of lever depends on the frame of reference. From the rower's perspective, the oar can be seen as a Class I lever. The oar is fixed in the oarlock, the rower pulls on the handle, and the blade moves in the opposite direction to propel the boat.