Friction is a force that opposes motion between any surfaces that are touching. It is defined as the resistance offered by the surfaces that are in contact when they move past each other. Friction can work for or against us. For example, putting sand on an icy sidewalk increases friction so you are less likely to slip. On the other hand, too much friction between moving parts in a car engine can cause the parts to wear out. There are four types of friction: static, sliding, rolling, and fluid friction (Air/Viscous friction) .

• Static Friction: This is the friction that acts between the surfaces when they are at rest with respect to each other.
• Sliding Friction: This is the resistance created between any two objects when sliding against each other.
• Rolling Friction: This is the friction that occurs when an object rolls over a surface.
• Fluid Friction: This is the friction that acts on objects that are moving through a fluid, such as liquids and gases.

Friction depends on the smoothness or roughness of the two surfaces that are in contact with each other. When the surface is smooth, the friction between the two reduces as there is not much interlocking of irregularities. While the surface is rough, friction increases.