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Friction, informally referred to as the force against all forces, is one of the most important and common forces in everyday situations. Friction is generated by two objects, at least one of them moving, rubbing against each other, with their non-entirely smooth surfaces.


Friction is what makes bike breaks stop safely, as well as vehicle tires. Friction can also be caused by air and water. When this occurs, the friction caused is usually referred to as drag. Drag is usually not taken much into account as thrust can easily dominate in a moving object impacted by drag.

Passenger planes

Passenger planes fly because of the forces their engines generate and/or increase - thrust and normal force. Normal force is locally increased within the plane’s area, letting the passenger plane lift off from the ground at speeds that dwarf Friction. The wheels are used only when needed and fall back within the plane, to spare them and reduce as much friction as possible.

Plane noses and wings reduce friction and loud sounds by their smooth-shaped noses and wings. Plane wings and noses are smooth, so they don't "cut" into the air and have the air beat down on them, but rather cause the air to flow around them.