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| | The author is known as Irwin. Bookkeeping is her day job now. To collect cash is what her family and her enjoy. Minnesota has usually been his house but his spouse desires them to transfer.<br><br>My blog post - home std test kit ([http://www.blaze16.com/blog/188254 why not try here]) |
| {{Unreferenced|date=December 2009}}
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| [[File:Rolling Racers - Moment of inertia.ogv|thumb|400px|right|Four objects racing down a plane while rolling without slipping. From back to front: spherical shell (red), solid sphere (orange), cylindrical ring (green) and solid cylinder (blue). The time for each object to reach the finishing line depends on their [[moment of inertia]] around the rolling axis. ([[:File:Rolling Racers - Moment of inertia.ogv|Details]], [[:File:Rolling Racers - Moment of inertia.gif|Animated GIF version]])]]
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| '''Rolling''' is a [[Motion (physics)#Types of motion|type of motion]] that combines [[rotation]] (commonly, of an [[Axial symmetry|axially symmetric]] object) and [[Translation (geometry)|translation]] of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact with each other without [[sliding (motion)|sliding]].
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| Rolling is achieved by a rotational speed at the line or point of contact which is equal to the translational speed. When no sliding takes place the rolling motion is referred to as 'pure rolling'. In practice, due to small deformations at the contact area, some sliding does occur. Nevertheless, [[rolling resistance]] is much lower than [[friction|sliding friction]], and thus, rolling objects, typically require much less [[energy]] to be moved than sliding ones. As a result, such objects will more easily move, if they experience a force with a component along the surface, for instance gravity on a tilted surface; wind; pushing; pulling; an engine. Unlike most axially symmetrical objects, the [[rolling cone motion|rolling motion of a cone]] is such that while rolling on a flat surface, its [[center of gravity]] performs a [[circular motion]], rather than a [[linear motion|linear]] one. Rolling objects are not necessarily axially-symmetrical. Two well known non-axially-symmetrical rollers are the [[Reuleaux triangle]] and the [[Reuleaux tetrahedron|Meissner bodies]]. Objects with corners, such as [[dice]], roll by successive rotations about the edge or corner which is in contact with the surface.
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| One of the most practical applications of rolling objects is the use of [[Rolling-element bearing]]s, such as [[ball bearings]], in rotating devices. Made of a smooth metal substance, the rolling elements are usually encased between two rings that can rotate independently of each other. In most mechanisms, the inner ring is attached to a stationary shaft (or axle). Thus, while the inner ring is stationary, the outer ring is free to move with very little [[friction]]. This is the basis for which almost all [[electric motor|motors]] (such as those found in ceiling fans, cars, drills, etc.) rely on to operate. The amount of friction on the mechanism's parts depends on the quality of the ball bearings and how much lubrication is in the mechanism.
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| Rolling objects are also frequently used as [[tools]] for [[transportation]]. One of the most basic ways is by placing a (usually flat) object on a series of lined-up rollers, or [[wheel]]s. The object on the wheels can be moved along them in a straight line, as long as the wheels are continuously replaced in the front (see [[bearing (mechanical)#History and development|history of bearings]]). This method of primitive transportation is efficient when no other machinery is available. Today, the most practical application of objects on wheels are [[cars]], [[trains]], and other human transportation vehicles.
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| The velocity of a particle in the rolling object is given by: <math>\mathrm{v}=r\times\omega</math>, where <math>r</math> is the distance between the particle and the rolling object's contact point (or line) with the surface, and <math>\omega</math> is the rolling object's angular velocity.
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| ==See also==
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| * [[Rolling resistance]]
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| * [[Frictional_contact_mechanics#Solution_of_rolling_contact_problems|Frictional contact mechanics: Rolling contact]]
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| * [[Terrestrial_locomotion_in_animals#Rolling|Terrestrial locomotion in animals: Rolling]]
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| * [[Tumbling (gymnastics)]]
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| [[Category:Rotation]]
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| [[ar:التدحرج]]
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| [[he:ערגול]]
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The author is known as Irwin. Bookkeeping is her day job now. To collect cash is what her family and her enjoy. Minnesota has usually been his house but his spouse desires them to transfer.
My blog post - home std test kit (why not try here)