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Related Concept Videos

Characteristics of Dry Friction01:21

Characteristics of Dry Friction

940
Dry friction occurs when two solid surfaces slide against each other without any lubrication or fluid present. It causes resistance when pushing objects along a surface, like a gardener pushing a wheelbarrow. The force applied to move the cart causes dry friction between the wheel and the ground.
Before the wheelbarrow starts moving, the static frictional force acts tangentially to the contact surface, opposing the force that is about to induce the motion. This frictional force prevents the...
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Static and Kinetic Frictional Force01:05

Static and Kinetic Frictional Force

25.0K
One of the simpler characteristics of sliding friction is that it is parallel to the contact surfaces between systems, and is always in a direction that opposes the motion or attempted motion of the systems relative to each other. If two systems are in contact and moving relative to one another, then the friction between them is called kinetic friction. For example, kinetic friction slows a hockey puck sliding on ice.
However, if two systems are in contact and are stationary relative to one...
25.0K
Types of Friction Problems01:27

Types of Friction Problems

922
Friction is an essential concept in physics, engineering, and everyday life. It is the force that opposes the relative motion or tendency of such motion between two surfaces in contact. One of the most common types of friction encountered in various applications is dry friction. Dry friction problems can be broadly categorized into three types, each with unique characteristics and challenges.
The first type of dry friction problem involves situations where there is no apparent impending motion....
922
Dry Friction01:30

Dry Friction

886
Dry friction occurs between two solid surfaces in contact as they attempt to move relative to one another. In daily life, dry friction is encountered in various forms, such as when walking on the ground, sliding an object across a table, or rubbing hands together. Despite its ubiquity, the underlying mechanisms behind dry friction are not readily visible.
To illustrate this concept, imagine a wooden crate resting on a rough, non-uniform horizontal surface. When an external force is applied to...
886
Kinetic Friction01:26

Kinetic Friction

1.4K
Consider a truck trying to pull a stationary car. As the truck exerts a force on the car, static friction is created at the point of contact between the two surfaces. This frictional force resists the car's movement and keeps it at rest. However, when the applied force by the truck surpasses the limiting static frictional force, an interesting phenomenon occurs. The frictional force at the interface reduces to a lower value, known as the kinetic frictional force. At this point, the car...
1.4K
Frictional Force01:07

Frictional Force

9.6K
When a body is in motion, it encounters resistance because the body interacts with its surroundings. This resistance is known as friction, a common yet complex force whose behavior is still not completely understood. Friction opposes relative motion between systems in contact, but also allows us to move. Friction arises in part due to the roughness of surfaces in contact. For one object to move along a surface, it must rise to where the peaks of the surface can skip along the bottom of the...
9.6K

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Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel
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Electrically Tunable Friction: From Sticky to Slippery with Ionic Hydrogels.

Chenxu Liu1,2, Yuan Yao1, Yuanyuan Wang1

  • 1Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 1H9, Canada.

Advanced Materials (Deerfield Beach, Fla.)
|December 4, 2025
PubMed
Summary

Researchers developed an electric-field strategy to control friction using ionic hydrogels. This method achieves over fifty-fold reversible friction modulation without lubricants, enabling energy-efficient adaptive systems.

Keywords:
crawling robotselectric fieldfriction controlionic polymersultra‐low friction

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Preparation and Friction Force Microscopy Measurements of Immiscible, Opposing Polymer Brushes
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Area of Science:

  • Materials Science
  • Robotics
  • Tribology

Background:

  • Controlling friction is key for energy efficiency and adaptive systems.
  • Current methods often require liquid lubricants and have limited modulation.
  • Macroscopic scale friction control faces challenges with sealing and practical application.

Purpose of the Study:

  • To introduce an electroresponsive material for tunable friction.
  • To demonstrate a lubricant-free method for significant friction modulation.
  • To explore applications in adaptive robotic systems.

Main Methods:

  • Utilized a polyvinyl alcohol-based ionic hydrogel as an electroresponsive material.
  • Applied low voltage control (-30 V to +30 V) to modulate friction during sliding against a metal ball.
  • Investigated the underlying mechanism of friction reduction via electroosmotic effects.

Main Results:

  • Achieved over a fifty-fold reversible modulation of the friction coefficient (COF).
  • Reduced COF to as low as 0.03 at -30 V, while increasing it to 1-2 at 0 V or +30 V.
  • Demonstrated electroosmotic extraction of a salt-rich interfacial layer as the mechanism for friction reduction.

Conclusions:

  • Developed a novel electric-field strategy for real-time friction control using ionic hydrogels.
  • Established a lubricant-free, voltage-controlled method for significant friction modulation.
  • Pioneered applications in a crawling robot and robotic arm, showcasing a new paradigm for adaptive, energy-efficient systems.