Friction

Friction Forces Resist Motion

Friction creates resistance between surfaces sliding against each other. This fundamental force affects everything from walking to machinery operation, accounting for about 20% of the world’s energy consumption.

Historical Development Shows Evolution

The study of friction spans over 2000 years. Leonardo da Vinci first documented the laws of sliding friction in 1493, though these findings remained unpublished. Guillaume Amontons rediscovered these principles in 1699, establishing the three core laws of dry friction that we use today.

Types Define Different Interactions

The main friction categories include:

• Dry friction between solid surfaces
• Fluid friction in liquids and gases
• Lubricated friction using intermediary substances
• Skin friction from fluid flow across surfaces
• Internal friction within deforming materials

Dry Friction Creates Resistance

Two key forms of dry friction exist:

• Static friction prevents stationary objects from moving
• Kinetic friction resists motion between sliding surfaces

The Coulomb model describes this using the equation: F = μN, where:

• F represents the friction force
• μ symbolizes the coefficient of friction
• N equals the normal force between surfaces

Modern Understanding Advances

Scientists now know friction occurs at microscopic levels. The actual contact area between surfaces comprises tiny points called asperities. These points determine the true friction force, explaining why rougher surfaces generally create more friction.

Applications Impact Daily Life

Friction plays crucial roles in:

• Vehicle braking systems
• Manufacturing processes
• Walking and movement
• Machine operation
• Energy conservation

The study of friction, called tribology, continues to advance our understanding of this essential force that affects virtually every aspect of mechanical interaction.

Citations:

https://en.wikipedia.org/wiki/Friction

Friction (Wikipedia)

For other uses, see Friction (disambiguation).

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of the processes involved is called tribology, and has a history of more than 2000 years.

Friction can have dramatic consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Another important consequence of many types of friction can be wear, which may lead to performance degradation or damage to components. It is known that frictional energy losses account for about 20% of the total energy expenditure of the world.

As briefly discussed later, there are many different contributors to the retarding force in friction, ranging from asperity deformation to the generation of charges and changes in local structure. Friction is not itself a fundamental force, it is a non-conservative force – work done against friction is path dependent. In the presence of friction, some mechanical energy is transformed to heat as well as the free energy of the structural changes and other types of dissipation, so mechanical energy is not conserved. The complexity of the interactions involved makes the calculation of friction from first principles difficult and it is often easier to use empirical methods for analysis and the development of theory.