How is friction increased and decreased?

Answer 1

It is when the surface areas in contact increase or decrease. With increased surface areas in contact, friction increases.
The faster an object moves against another object, the greater the friction will increase. Same basic principle can be applied for the decrease in friction, by slowing down movement. For example, humans stay grounded tongue ground do to the force of gravity, in which the earth is spinning very fast but you can't feel it, the force of the earth spinning (friction) causes gravity to hold us to the ground.
Friction, as a physical term, is the force that opposes to movement when two objects contact each other in the shpere of cinematics. It is produced by the contact between atoms. Friction as a physical property cannot be decreased nor increased. But, by placing other object between these initial two can give different friction between those two, reducing the force that opposes to movement and therefore, at the end of the ecuation, reducing friction.
Increase friction by having rougher surfaces rubbing together. Decrease friction by having smoother surfaces rubbing together. Remove oil or grease to increase friction. Add oil or grease to reduce friction.
Classical friction depends on two factors: weight and friction coefficient. When decreasing weight is usually problematic or impossible, friction can be decreased by lowering the friction coefficient. For this purpose different kinds of surfactants and oils are used or even air.
to decrease friction you need to use lubricants,while to increase friction you need to use breaks
you incraese friction when something is sticke and hard to slide on each other.

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By decreasing area of friction and using oils of friction surface.

Answer 2

Friction is increased by increasing the roughness of the surfaces in contact, increasing the force pressing the surfaces together, and increasing the surface area in contact. Friction can be decreased by using lubricants that reduce contact between surfaces, using smoother surfaces, and reducing the force pressing the surfaces together.