Roda

From Wikipedia

Satu roda pacuan pada lokomotif stim .

Roda merupakan objek bulat yang dilengkapi dengan gandar(axle), yang membolehkan pergerakan dengan geseran yang minima dengan bergolek. Roda biasanya digunakan didalam applikasi pengangkutan. Secara umumnya, istilah roda juga digunakan bagi objek bulat berputar bagi tujuan lain, seperti roda melarik tembikar.

[Sunting] Mekanik

Roda digunakan bersama gandar, samaada roda berpusing pada gandar ataupun tayar dilekatkan terus pada gandar yang kemudiannya berputar dalam bering pada badan kenderaan. Mekanismanya adalah sama dalam kedua-dua kes.

Geseran rendah (berbanding diheret) dijelaskan seperti berikut:

jarak geluncur dikurangkan, kerana seretan berlaku antara roda dan gandar atau antara gandar dengan bearing
koefisyen geseran kinetik μ bagi geseran adalah kurang for sliding the friction is less

Rencana ini diterjemahkan daripada sebahagian rencana Wikipedia bahasa Inggeris. Bantulah Wikipedia menterjemahkan* lagi seperenggan dua. Bahan-bahan boleh didapati di en:wheel*.
Terima kasih kerana membaca rencana ini. Sumber bantuan: Kamus Dewan Bahasa

Contoh:

Sekiranya mengheret 100 objek kg sejauh 10 m pada permukaan dengan μ = 0.5, tenaga normal pada Bumi ialah 980 N dan kerja yang dilakukan (memerlukan tenaga) 980 × 10 × 0.5 = 4900 joule.
Jika diambil objek beroda 4. Kuasa biasa antara 4 roda dan gandar adalah sama (keseluruhan) 980 N, dianggap μ = 0.1, akhirnya faktor paling penting adalah dimeter roda (1000 mm) dan axle diameter (50 mm). Now while the object still moves 10 m the sliding frictional surfaces only slide over each other a distance of 0.5 m. So work done is 980 x 0.5 x 0.1 = 49 joules.

Additional energy is lost at the wheel to road interface (rolling friction), but it is deformation loss which can be very small. An example would be train wheels on rail tracks). The tradeoff is that a wheeled object in motion carries more momentum than dragging, and thus require an external force in the opposite direction in order to stop the object or change its direction, for example, such as brakes.

[Sunting] Sejarah roda

A depiction of onager-drawn carts on the Sumerian "battle standard of Ur" (circa 2600 BC)

According to most authorities, the wheel was invented in ancient Mesopotamia in 3000 BC, originally in the function of potter's wheels. A possibly independent invention in China dates to around 2800 BC. It is also thought that the invention of the wheel dated back to Ancient India. Though they did not develop the wheel proper, the Inca and certain other western hemisphere cultures seem to have approached the concept, as wheel-like worked stones have been found on objects identified as children's toys dating to about 1500 BC. The wheel was apparently unknown in sub-Saharan Africa, Australia, and the Americas until relatively recent contacts with Eurasians.

A spoked wheel on display at The National Museum of Iran, in Tehran. The wheel is dated late second millennium BCE and was excavated at Choqa Zanbil.

The invention of the wheel thus falls in the late Neolithic and may be seen in conjunction with the other technological advances that gave rise to the early Bronze Age. Note that this implies the passage of several wheel-less millennia, even after the invention of agriculture. Early wheels were simple wooden disks with a hole for the axle. The spoked wheel was invented much more recently, and allowed the construction of lighter and swifter vehicles. The earliest known examples are in the context of the Andronovo culture, dating to ca 2000 BC (see chariot). Celtic chariots introduced an iron rim around the wheel in the 1st millennium BC. The spoked wheel was in continued use without major modification until the early 20th century.

The invention of the wheel turned out to be of great importance not only as a transportation device, but for the development of technology in general, important applications including the water wheel, the cogwheel (see also antikythera mechanism), the spinning wheel, the astrolabe or torquetum. More modern descendents of the wheel include the propeller, the jet engine, the flywheel (gyroscope) and the turbine.

The central importance of the wheel also resulted in its becoming a strong cultural and spiritual metaphor for a cycle or regular repetition (see chakra, reincarnation).

In July 2001, the wheel was the object of an innovative, but non-inventive, patent as a "circular transportation facilitation device" [1]. The patent was obtained by John Keogh, a lawyer from Melbourne, Australia, with the declared intention of demonstrating the unfairness and inaccuracy of the modern patent system.