Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Friction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed2005

A generic mechanism of sliding friction between charged soft surfaces.

A universal sliding friction mechanism between soft, electrically charged surfaces (e.g., those carrying polyelectrolytes) is proposed. The Coulomb field of the randomly distributed charges induces a damped motion of the charges of the opposite surface, which gives rise to dissipation, and thus to friction. It is predicted that this friction force, which diverges at zero separation, may overcome viscous friction at distances significantly exceeding the Bjerrum length. This is not only of fundamental interest, but also of potential importance in life science and many practical situations.

Journal Article↗
PubMed2006

Superconductivity dependent friction of water, nitrogen, and superheated He films adsorbed on Pb(111).

We report a quartz crystal microbalance study of sliding friction levels in N2, H2O, and superheated He films adsorbed on Pb(111) substrates alternating in and out of the superconducting state. Reductions in friction upon entry into the superconducting state are greater for N2 than He, consistent with a recent theory that linked electronic friction to adsorbate polarizability. Our work also reveals that repetitive cycling of an externally applied magnetic field may impact friction.

Journal Article↗
PubMed1977

Frictional properties of skin.

To gain a more fundamental understanding of the frictional properties of skin, various parameters (hydration, oils, surfactants, etc) affecting skin friction were evaluated using a rotational friction technique. The rotational device utilized a motor-driven wheel. The wheel and drive shaft were connected to the motor through a flexible rubber coupling in such a way that friction encountered by the wheel caused a lateral displacement of the drive shaft which was monitored by a photocell and recorded on a strip-chart recorder.

Biophysical Phenomena↗
PubMed1990

Frictional properties of human skin: relation to age, sex and anatomical region, stratum corneum hydration and transepidermal water loss.

Differences in the dynamic skin friction coefficients (mu) were investigated with respect to age, sex, and anatomical region. A total of 29 volunteers consisting of seven young females, seven old females, seven young males, and eight old males participated in the study. Measurements were obtained from II anatomical regions, namely, the forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper and lower back, thigh, and ankle. The friction data were compared with stratum corneum hydration and transepidermal water loss (TEWL). The dynamic friction coefficient did not vary significantly between age and sex groups but varied considerably among the anatomical regions of the body. The forehead and postauricular had the highest mu (0.34 +/- 0.02) while the abdomen had the lowest (0.12 +/- 0.01); the remaining regions had an average mu value of 0.21 +/- 0.01. Similarly, no sex differences were observed for TEWL and stratum corneum hydration. Capacitance was only significantly lower on the palms of the elderly. Regional differences showed a higher state of hydration on the forehead and postauricular as well as the upper arm, upper and lower back when compared with the volar forearm. TEWL was generally lower in the elderly on all anatomical regions except the postauricular and palm. A significant correlation was established between mu and capacitance for most regions. Between mu and TEWL significant correlation was observed only on the palm and thigh. These findings suggest that frictional properties of skin are dependent on more than water content or non-apparent sweating and the role of sebum secretion is suggested as one possible factor.

Adult↗
PubMed1990

Evaluation of a new device for measuring oral mucosal surface friction.

For the objective measurement of oral mucosal dryness or moisture, a device registering oral mucosal surface slide friction has been developed. Two prototypes, Probe I and Probe II, have been tested. Probe I was constructed for initial testing of the method and was based on easily accessible electrical components. Probe I was computerized and developed for more accurate registration and also for easy handling. Reliability and validity tests were carried out on Probe I as well as on Probe II. In repeated in vitro measurements, the probes showed good reproducibility. Validity was assessed on healthy subjects injected with methylscopolamine nitrate submucosally in the labial sulcus. All subjects experienced a pronounced oral mucosal dryness within half an hour. Registration with the surface slide friction device showed maximum friction values 1-2 h after injection. These reliability and validity tests gave good results for both Probe I and Probe II, but Probe II had several practical advantages over Probe I. Both probes were considerably more sensitive to changes of the oral mucosal surface than the previously used simple friction test using the back of a mouth mirror.

Adult↗
PubMed2000

Reconstruction of bowing point friction force in a bowed string

A method is presented for reconstructing the friction force and the velocity at the bowing point of a string excited by a rosined bow sliding transverse to the string. Two versions of the method of reconstruction are presented, each approximate in different ways, but both capable of sufficient accuracy to allow useful application to problems of understanding frictional interactions in this dynamical system. The method is illustrated with simulated data to verify its accuracy, and results are shown for two contrasting cases of observed stick-slip string motion. As has been found in other investigations, the friction force during sliding is not determined by the instantaneous sliding speed. The results seem to be compatible with a thermally based model of rosin friction.

Journal Article↗
PubMed1999

Adsorbed layers and the origin of static friction

Analytic results and experiments in ultrahigh vacuum indicate that the static friction between two clean crystalline surfaces should almost always vanish, yet macroscopic objects always exhibit static friction. A simple and general explanation for the prevalence of static friction is proposed. "Third bodies," such as small hydrocarbon molecules, adsorb on any surface exposed to air and can arrange to lock two contacting surfaces together. The resulting static friction is consistent with experimental behavior, including Amontons' laws.

Journal Article↗
PubMed2003

Self-healing slip pulses and the friction of gelatin gels.

We present an extensive experimental study and scaling analysis of friction of gelatin gels on glass. At low driving velocities, sliding occurs via propagation of periodic self-healing slip pulses whose velocity is limited by collective diffusion of the gel network. Healing can be attributed to a frictional instability occurring at the slip velocity V=Vc. For V>Vc, sliding is homogeneous and friction is ruled by the shear-thinning rheology of an interfacial layer of thickness of order the (nanometric) mesh size, containing a solution of polymer chain ends hanging from the network. In spite of its high degree of confinement, the rheology of this system does not differ qualitatively from known bulk ones. The observed ageing of the static friction threshold reveals the slow increase of adhesive bonding between chain ends and glass. Such structural ageing is compatible with the existence of a velocity-weakening regime at velocities smaller than Vc, hence with the existence of the healing instability.

Journal Article↗
PubMed1989

Friction in femoral prosthesis and photoelastic model cone taper joints.

Static axial push-on and lift-off, and push-on and twist-off experiments were designed and performed to measure the effective, room-temperature coefficient of friction mu for different design femoral prosthesis cone taper joints comprising a universal head on a stem spigot. Alumina and metal heads were tested on metal spigots using either distilled water, Ringer's solution, blood or no lubricant. Complementary push-on and lift-off friction tests of Araldite model joints for subsequent frozen-stress, photoelastic stress analysis were performed at 130 degrees C. It was found that lubricant caused little decrease in the values of the coefficient of friction in prosthesis tapers. The values measured were typically mu = 0.2 for an alumina head on a Co-Cr-Mo or Ti-6Al-4V spigot, mu = 0.15 for a Co-Cr-Mo head on a Co-Cr-Mo or Ti-6Al-4V spigot and mu = 0.13 for a stainless steel head on a stainless steel spigot. For Araldite photoelastic models of an alumina head on a Vitallium spigot, as-cast taper surfaces lubricated with silicone grease gave consistent friction of typically mu = 0.14. The axial displacement of model heads on their spigots were compared with predicted values and previously measured values for prosthesis heads.

Epoxy Resins↗
PubMed2006

Effects of vision and friction on haptic perception.

OBJECTIVE: Two experiments were conducted to examine the effects of vision and masking friction on contact perception and compliance differentiation thresholds in a simulated tissue-probing task. BACKGROUND: In minimally invasive surgery, the surgeon receives limited haptic feedback because of the current design of the instrumentation and relies on visual feedback to judge the amount of force applied to the tissues. It is suggested that friction forces inherent in the instruments contribute to errors in surgeons' haptic perception. This paper investigated the psychophysics of contact detection and cross-modal sensory processing in the context of minimally invasive surgery. METHOD: A within-subjects repeated measures design was used, with friction, vision, tissue softness, and order of presentation as independent factors, and applied force, detection time, error, and confidence as dependent measures. Eight participants took part in each experiment, with data recorded by a custom force-sensing system. RESULTS: In both detection and differentiation tasks, higher thresholds, longer detection times, and more errors were observed when vision was not available. The effect was more pronounced when haptic feedback was masked by friction forces in the surgical device (p < .05). CONCLUSION: Visual and haptic feedback were equally important for tissue compliance differentiation. APPLICATION: A frictionless endoscopic instrument can be designed to restore critical haptic information to surgeons without having to create haptic feedback artificially.

Adult↗
PubMed1990

[Friction sound as an objective sign of completion of root planing].

Root planing is one of the most important procedures in periodontal treatment. However, there are no objective clinical signs to indicate completion of this procedure. The purpose of this study was to examine the friction sound produced by curettes and root surfaces during root planing and to test the possibility of utilizing the sound changes as an objective parameter for evaluating completion of the procedure. The study consisted of a clinical and laboratory experiment. Seven periodontally diseased teeth were utilized in the clinical trial. During scaling and root planing with the Gracey curette, the friction sound was clinically analyzed with a sound spectrograph. The root surface, in situ, was observed by scanning electron microscopy (SEM) with the replica technique. Twenty-one periodontally diseased teeth were used in the laboratory study. Root planed surfaces were classified as pre-root planed and post-root planed according to their friction sounds during root planing. Each surface was examined by the following methods: 1) measuring root surface roughness 2) SEM observations 3) determination of number of adherent cells by the cultured fibroblast technique. As a result, post-root planed surfaces were well root planed as evaluated by SEM observations and the profilometer. Similarly, adherent cell counts were increased on post-root planed surfaces. These results indicated the possible usefulness of friction sound analysis to judge the completion of root planing.

Cell Adhesion↗
PubMed2002

Frictional torque and wear of retrieved hip prostheses: a comparison between alumina/PE and Co-Cr/PE prostheses.

Frictional torque and wear were measured in 67 retrieved cups with internal diameters of 32 mm. Thirty cups were combined with alumina heads and 37 were combined with metal heads. A lower prevalence of cup loosening was observed in alumina-polyethylene implants than in metal-polyethylene implants. No relation between frictional torque and stability of implants was detected for either type, whereas retrieved cups of alumina-polyethylene implants showed lower frictional torque than those of metal-polyethylene implants. Less wear was observed in the cups of alumina-polyethylene implants (0.13 mm/y) than in those of metal-polyethylene implants (0.19 mm/y). Less wear was observed in cups without loosening than in those with loosening in both types. These results suggest that wear has a greater influence on the stability of cups than frictional torque.

Adult↗
PubMed1992

Iliotibial band friction syndrome as exhibited in athletes.

Iliotibial band (ITB) friction syndrome is an overuse injury common in runners, cyclists, weight lifters, skiers, and soccer players. It is characterized by pain over the lateral femoral epicondyle caused by excessive friction between the ITB and the lateral femoral epicondyle.ITB friction syndrome can be prevented by using correct mechanics and training practices. Avoiding such errors, such as a swift change in playing surfaces or running excessive distances, can prevent this condition. Orthotics to correct mechanical problems also can prevent this injury. Stretching is not only a good treatment, it also is a good prophylaxis. Rest and the application of therapeutic modalities resolve most cases of ITB friction syndrome, but, in persistent cases, surgical intervention may be considered.

Journal Article↗
PubMed2000

Corrective neuromuscular approach to the treatment of iliotibial band friction syndrome: a case report.

OBJECTIVE: To describe the evaluation and treatment process for inappropriate functional patterns of neuromuscular activity within the scope of an iliotibial band friction syndrome protocol. BACKGROUND: Runners with iliotibial band friction syndrome are frequently fitted with orthotic devices to restrict excessive midfoot or rearfoot, or both, motions during the stance phase. These devices may fail to yield favorable results when underlying neuromuscular factors are associated with functional iliotibial band tightening. DIFFERENTIAL DIAGNOSIS: Distal biceps femoris tendinitis, popliteal tendinitis, lateral meniscus lesion. TREATMENT: The athlete's physical examination revealed several patterns of inappropriate neuromuscular activity attributed partly to the prolonged daily wear of beach-type sandals. Modifications of casual footwear and a temporary reduction in training volume were recommended initially to prevent exacerbation of the athlete's condition. Stretching, massage, and soft tissue mobilization were administered in accordance with the athlete's specific needs. The protocol included progressions of nonweightbearing and weightbearing therapeutic exercises. Neuromuscular electric stimulation was incorporated into the protocol to re-educate the role of the first ray within the stance phase of the athlete's walking gait. UNIQUENESS: Upon stationary examination, this athlete presented with normal lumbar and lower extremity postures. Gait analysis, however, revealed inappropriate dorsiflexion of the great toe during ambulation. Further, the athlete's performances on a series of tests to assess neuromuscular function were substandard. This athlete's response to previous treatment and unique physical findings required a corrective neuromuscular approach that deviates from iliotibial band friction syndrome protocols advocating the use of orthotics. CONCLUSIONS: While the role of any single treatment in the athlete's recovery remains unknown, it seems that a corrective neuromuscular approach in the management of iliotibial band friction syndrome represents a viable alternative to orthotic intervention.

Journal Article↗
PubMed1989

[The biological role of the structural-deformable properties of the cartilage and of the synovial fluid in the reduction of intra- articular friction].

The authors have studied the problem of low friction of biopolymers. The most common approaches to the explanation of the mechanism of joint lubrication are characterized. It has been demonstrated that the role of elastohydrodynamic action during the friction of the cartilages is insignificant. On the basis of the experimental data a comparison of the structural and mechanical and anti-friction++ properties of the synovial medium has been made. It has been demonstrated that the results obtained, taking into consideration the regularity of the surface layers structure and the deformation properties of the cartilage testify in favour of the previous suggestion concerning the influence of the liquid crystal compounds on low friction and wear in the joint.

Animals↗
PubMed1993

The influence of conformity and constraint on translational forces and frictional torque in total shoulder arthroplasty.

Glenoid loosening in total shoulder arthroplasty (TSA) may result from translational forces and frictional torque generated at the articular surfaces and transmitted to the fixation interface. The effect of glenohumeral articular design on the magnitude of these translational forces and frictional torques has not been evaluated previously. Seven different glenohumeral designs were evaluated on a specially designed fixture integrated with a materials test system. The degree of conformity and constraint in the glenohumeral designs directly affected the forces generated during translation and rotation of the humeral head. Maximum translational forces occurred close to the midline in the more conforming design. The less conforming designs generated lower translational forces and frictional torques. Because frictional torque and translational forces at the glenohumeral articulation may contribute to glenohumeral loosening, the use of less conforming and less constrained designs is advocated where possible to reduce the potential for mechanical loosening of the glenoid component.

Biomechanical Phenomena↗
PubMed2007

Reduced expression and proteolytic susceptibility of lubricin/superficial zone protein may explain early elevation in the coefficient of friction in the joints of rats with antigen-induced arthritis.

OBJECTIVE: To investigate the effect of arthritis development and progression on the integrity and function of lubricin and the relationship of lubricin to cartilage damage in a rat antigen-induced arthritis model. METHODS: Arthritis was induced in the right knee joints, using methylated bovine serum albumin and Freund's complete adjuvant. Whole joint friction measurements were performed ex vivo with a modified Stanton pendulum configuration, and coefficients of friction (mu) were determined. Levels of messenger RNA (mRNA) for lubricin, cathepsin B, and interleukin-1beta (IL-1beta) in synovial tissue from control and affected joints were determined by quantitative polymerase chain reaction. Lubricin staining in cartilage was performed using a lubricin-specific monoclonal antibody. RESULTS: The mu values in excised right joints following arthritis induction were significantly (P < 0.001) higher than those in excised left joints. Lubricin mRNA expression levels in synovial tissue on days 4 and 7 after arthritis induction were significantly (P < 0.001) lower in the right joints compared with the left joints, whereas levels of cathepsin B and IL-1beta mRNA expression on days 4, 7, and 14 were significantly (P < 0.001) higher in the right joints than the left joints. Lubricin staining was diminished in cartilage from the right joints compared with the left joints. CONCLUSION: Elevated coefficients of friction in arthritic joints occur concurrently with enhanced proteolytic degradation by up-regulated cathepsin B and other proteases, as well as decreased lubricin synthesis by synovial fibroblasts and superficial zone chondrocytes. Loss of joint lubrication is an early event in inflammatory arthropathy. Restoring chondroprotection and preventing potential wear-induced cartilage degradation may require lubricin supplementation in synovial fluid.

Adjuvants, Immunologic↗
PubMed1993

[Frictional forces and movement dynamics in the mesialization of the second molar after the extraction of the sixth-year molar. An in-vitro study].

In this study the frictional forces and dynamics of arch guided molar mesialization were investigated. The influence of two different slot/arch combinations (.018" slot/.016" x .022" arch and .022" slot/.019" x .025" arch) as well as partial fortification of an .016" x .022" wire and the reduction of interbracket distance were studied. In guiding the arch wire, a convertible bracket was tested in tube and in bracket configurations. The tipping movement could be compensated by adding an uprighting spring. The orthodontic measurement and simulation system (OMSS) was employed to determine frictional loss in forces and to analyze side effects. Results showed that frictional forces were almost independent from the wire stiffness, whereas a reduced cross section resulted in distinct side effects. These effects can be countered either by employing a correctly dimensioned uprighting spring or by increasing the wire stiffness. The .019" x .025" wire in a .022" slot proved to be the optimum combination for molar mesialization.

Biomechanical Phenomena↗