Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the term "static friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

", perhaps also influenced by the verb "stick
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....


Any solid objects pressing against each other (but not sliding) will require some threshold of force parallel to the surface of contact in order to overcome static cohesion. Stiction is a threshold, not a continuous force.

In situations where two surfaces with areas below the micrometer range come into close proximity (as in an accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...

), they may adhere together. At this scale, electrostatic and/or Van der Waals
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...

 and hydrogen bonding forces become significant. The phenomenon of two such surfaces being adhered together in this manner is also called stiction. Stiction may be related to hydrogen bonding or residual contamination.


Place a wooden block near one end of a long wooden board. Leaving the far end of the board on the floor, lift the end with the block until the slope of the board is sufficient for the block to begin sliding downward without being pushed. Then lower the board slightly.

Placing the block again at the top, it will not begin to slide on its own. However, it will begin and continue to slide if given a small initial push. The push adds the necessary force to overcome stiction. Once the block is moving, it no longer requires the larger force.


Stiction is also the same threshold at which a rolling object would begin to slide over a surface rather than rolling at the expected rate (and in the case of a wheel, in the expected direction). In this case, it's called "rolling friction" or μr.

This is why driver training courses teach that if a car begins to slide sideways, the driver should try to steer in the same direction as the slide with no brakes. It gives the wheels a chance to regain static contact by rolling, which gives the driver some control again. An overenthusiastic driver may "squeal" the driving wheels trying to get a rapid start but this impressive display of noise and smoke is less effective than maintaining static contact with the road. Many stunt
A stunt is an unusual and difficult physical feat, or any act requiring a special skill, performed for artistic purposes in TV, theatre, or cinema...

-driving techniques are also done by deliberately breaking and/or regaining this rolling friction.

A car on a slippery surface can slide a long way if the driver "locks" the wheels in stationary positions by pressing hard on the brakes. Anti-lock braking system
Anti-lock braking system
An anti-lock braking system is a safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up and therefore avoiding skidding.An ABS generally offers...

s use wheel speed sensors and vehicle speed sensors to determine if any of the wheels have stopped turning. The ABS Module then briefly releases pressure to that wheel to allow the wheel to begin turning again. Anti-lock brakes can be much more effective than cadence braking
Cadence braking
Cadence braking or stutter braking is an advanced driving technique used to allow a car to both steer and brake on a slippery surface. It is used to effect an emergency stop where traction is limited, to reduce the effect of skidding from road wheels locking up under braking...

 which is essentially a non-automatic technique for doing the same thing.

Surface micromachining

Stiction or adhesion between the substrate (usually silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 based) and the microstructure occurs during the isotropic wet etching
Wet etching
Wet etching may refer to:*Industrial etching*Etching...

 of the sacrificial layer. The capillary forces
Capillary action
Capillary action, or capilarity, is the ability of a liquid to flow against gravity where liquid spontanously rise in a narrow space such as between the hair of a paint-brush, in a thin tube, or in porous material such as paper or in some non-porous material such as liquified carbon fiber, or in a...

 due to the surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 of the liquid between the microstructure and substrate during drying of the wet etchant cause the two surfaces to adhere together. Separating the two surfaces is often complicated due to the fragile nature of the microstructure. Stiction is often circumvented by the use of a sublimating fluid (often supercritical
Supercritical may refer to:* Critical mass, the smallest amount of fissile material needed for a sustained nuclear chain reaction* Critical temperature, Tc, the temperature above which distinct liquid and gas phases do not exist...

 , which has extremely low surface tension) drying process where the liquid phase is bypassed. displaces the rinsing fluid and is heated past the supercritical point. As the chamber pressure is slowly released the sublimates thereby preventing stiction.

Hard disk drives

In the context of hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...

 drives, stiction refers to the tendency of read/write heads
Disk read-and-write head
Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...

 to stick to the platters
Hard disk platter
A hard-disk platter is a component of a hard-disk drive: it is the circular disk on which the magnetic data is stored. The rigid nature of the platters in a hard drive is what gives them their name . Hard drives typically have several platters which are mounted on the same spindle...

. Stiction as a result of smoothness and is exacerbated by humidity and other liquids condensing at the head-disk interface. Once the heads have stuck to the platters, the disk can be prevented from spinning up and can cause physical damage to the media and the slider. Other forces considered as responsible for stiction include electrostatic forces.

In the early models of hard disk drives stiction was known to cause read/write heads to stick the platters of the hard drive due to the breakdown of lubricants used to coat the platters. During the late 1980s and early 1990s as the size of hard drive platters decreased from the older 8" and 5.25" sizes to 3.5" and smaller, manufacturers continued to use the same calendering processes and lubricants used on the older, larger drives. The much tighter space caused much higher internal operating temperatures in these newer smaller drives, often leading to an accelerated breakdown of the surface lubricants into their much stickier components. When the drive was powered off and would cool down(say at the end of the day when a user went home and shut off their PC), these now-broken-down lubricants would become quite viscous and sticky, sometimes causing the read/write heads to literally stick to the platter. The common solution to this problem was the counter-intuitive move of taking the affected drive out of the host system, striking it gently, but firmly on the side against a desk or something as laterally as possible and then re-install it in the host system. This would break the heads free of the goop long enough to power the system back on, have the drive spin up and recover whatever data could be retrieved off it. While the data was retrieved, the machine would be left on constantly so that the heat from the drive's internals would keep the decaying lubricants in a liquid state.

Modern hard drives have mostly solved the stiction problem by using ramps to "unload" the heads from the disk surface on power-down. These ramps ensure the heads are not touching the platters, which not only prevents stiction but also keeps abrasion from kicking up microscopic particulates that can later contaminate the drive mechanism. Parking the heads in this manner also allows the voice coil actuator to be shut down to save power, so the heads are also frequently unloaded when the drive is idle. A competing solution is based on laser textured landing zones near the ID of the platter where no data is stored. The heads are parked in that zone and the actuator is latched until the next start-up. The landing zone consists of a controlled array of nanometer-level 'bumps' on the disk surface produced during manufacturing of the disk using a local substrate melting process employing suitable laser-based equipment. The method was pioneered by IBM around 1995 and is still widely in use in most desktop and server class HDDs.

Digital storage tapes

Stiction may also manifest itself on computer tape
Magnetic tape data storage
Magnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...

s (9 track tape etc.). The magnetic surface of the tape would be heated against the read head in the tape deck, and when the tape stopped moving would cool slightly and "glue" onto the read head. This could be avoided by configuring the software so that the tape could be read continuously.
Discussion by data recovery firm

Amateur astronomy

Additionally, the term has come into use in amateur astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 circles to describe a characteristic of Dobsonian style Altazimuth mount
Altazimuth mount
An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...

s. These mounts can resist initial movement by the user, making it difficult to track an object in the sky. Breaking this resistance requires enough force to cause the observer to overshoot the object.


Typically the phenomenon occurs when “green” epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....

 photopolymer components are left in direct contact with each other. If left long enough it appears that “cross-linking” of the polymer takes place in the region of contact. This effectively “welds” or more appropriately “glues” the parts together. This issue can have a significant impact on models where testing of kinematics are required. To avoid stiction in stereolithography
Stereolithography is an additive manufacturing technology for producing models, prototypes, patterns, and in some cases, production parts.-Technology description:...

 clean and more importantly “fully” cure all geometry prior to assembly.

Game show

In the TV Series Takeshi's Castle
Takeshi's Castle
was a Japanese game show that aired between 1986 and 1989 on the Tokyo Broadcasting System. It featured the Japanese actor Takeshi Kitano as a count who owns a castle and sets up impossible challenges for players to get to him. The show has become a cult television hit around the world...

, contestants must run over numerous rollers to reach the other side without falling. Depending on the athlete's balance and weight, some are able to scale across without creating too much rolling movement, whilst others break the stiction point, create the rolling motion, and fall early on.
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