# Friction torque

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{{short description|Torque caused by frictional forces}}[[Image: Example of friction torque.jpg|thumbnail|250px|This image displays an example situation where there is an active frictional torque. The large black [vector](/source/Vector_(geometric)) arrow represents the primary [force](/source/force) acting on the bar (the thick black line), causing it to rotate around the gray dot at its opposite end which represents an [axle](/source/axle). The large red vector arrow represents the [torque](/source/torque) caused by the primary force. The small black vector arrow represents the [frictional force](/source/Friction) caused by the bar sliding across the second bar (grey).]]

In [mechanics](/source/mechanics), '''friction torque''' is the [torque](/source/torque) caused by the [frictional force](/source/friction) working in [couple](/source/couple_(mechanics)) that occurs when two objects in contact move.<ref>{{Cite book |last1=Fischer |first1=Alfons |url=https://books.google.com/books?id=MjAdBDZf7WkC&dq=%22Friction+torque%22&pg=PA565 |title=Friction, Wear and Wear Protection |last2=Bobzin |first2=Kirsten |date=2011-02-10 |publisher=John Wiley & Sons |isbn=978-3-527-62852-0 |language=en}}</ref> Like all torques, it is a rotational force that may be measured in [newton meter](/source/newton_meter)s or pounds-feet.

==Engineering==
{{Citation needed section|date=February 2024}}
Friction torque can be disruptive in [engineering](/source/engineering). There are a variety of measures [engineers](/source/engineers) may choose to take to eliminate these disruptions. [Ball bearings](/source/Ball_bearings) are an example of an attempt to minimize the friction torque.<ref>{{Citation |last=Bloch |first=Heinz P. |title=Rolling Element Bearings and Lubrication* |date=1992-01-01 |work=Centrifugal Pumps (Second Edition) |pages=524–555 |editor-last=Lobanoff |editor-first=Val S. |url=https://www.sciencedirect.com/science/article/abs/pii/B9780080500850500230 |access-date=2024-12-02 |place=Boston |publisher=Gulf Professional Publishing |isbn=978-0-08-050085-0 |editor2-last=Ross |editor2-first=Robert R.}}</ref>

Friction torque can also be an asset in engineering.  Bolts and nuts, or screws are often designed to be fastened with a given amount of torque, where the friction is adequate during use or operation for the bolt, nut, or screw to remain safely fastened.  This is true with such applications as lug nuts retaining wheels to vehicles, or equipment subjected to vibration with sufficiently well-attached bolts, nuts, or screws to prevent the vibration from shaking them loose.<ref>{{Cite web |date=2019-04-05 |title=How to Prevent Vibrational Loosening |url=https://provenproductivity.com/why-fasteners-fail-how-to-prevent-vibrational-loosening/ |access-date=2024-12-02 |website=provenproductivity.com}}</ref>

==Examples==
*When a cyclist applies the brake to the forward wheel, the bicycle tips forward due to the frictional torque between the wheel and the ground.<ref>{{Cite web |last=Allen |first=John |date=2024-12-02 |title=Understanding torque as it applies to bicycles |url=https://sheldonbrown.com/twist.html |access-date=2024-02-12 |website=sheldonbrown.com}}</ref>
*When a golf ball hits the ground it begins to spin in part because of the friction torque applied to the golf ball from the friction between the golf ball and the ground.<ref>{{Cite web |last=Normani |first=Franco |title=Physics Of Golf |url=https://www.real-world-physics-problems.com/physics-of-golf.html |access-date=2024-12-02 |website=Real World Physics Problems}}</ref>

== References ==
{{Reflist}}

==See also==
* [Torque](/source/Torque)
* [Force](/source/Force)
* [Engineering](/source/Engineering)

Category:Mechanics
Category:Moment (physics)

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Adapted from the Wikipedia article [Friction torque](https://en.wikipedia.org/wiki/Friction_torque) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Friction_torque?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.