Engineering Mechanics Practice Test: Friction — Flashcards

Friction topics include: Dry friction characteristics and problems, wedges, frictional forces on screws, flat belts, pivot bearings and disks, journal bearings and rolling resistance.

Friction is a force that resists motion when an object's surface comes into contact with another surface. It's a retarding force that always acts in the opposite direction of motion. 
In engineering mechanics, friction is a crucial concept that represents the energy lost when two surfaces slide or roll over each other. This energy is typically lost as heat, so engineers try to minimize friction. 
The maximum frictional force between two surfaces is FMAX=μR, where μ is the coefficient of friction and R is the normal reaction between the two surfaces. 

There are four main types of friction: Static friction, Sliding friction, Rolling friction, Fluid friction. 
Friction reduces the mechanical advantage of a machine, which is the ratio of output to input.

Dry friction, also known as Coulomb friction, is a force that occurs when two solid surfaces in contact try to move relative to each other. The friction force opposes the relative velocity direction and depends on the normal force that acts on the body. 

Dry friction is subdivided into static friction and kinetic friction:
Static friction: Also known as "stiction", this occurs between non-moving surfaces.
Kinetic friction: This occurs between moving surfaces. 
Dry friction can be encountered in daily life, such as when walking on the ground, sliding an object across a table, or rubbing hands together.