Friction is a force that resists the relative motion between two objects or materials. The causes of this resistive force are molecular adhesion, surface roughness, and deformations. Adhesion is the molecular force resulting when two materials are brought into close contact with each other.

Causes of Friction
Friction is the force that opposes the relative motion or tendency of such motion of two surfaces in contact. There are several factors that contribute to the occurrence of friction.

Surface Roughness
- The rougher the surface of an object, the greater the friction between the surfaces in contact.
- Irregularities on the surfaces interlock with each other, causing resistance to motion.

Weight of the Objects
- Heavier objects have more force pressing them against each other, leading to greater friction.
- The weight of an object affects the normal force between the surfaces.

Surface Material
- Different materials have different levels of friction when in contact with each other.
- Smooth surfaces like ice have low friction, while rough surfaces like sandpaper have high friction.

Temperature
- Temperature can affect the level of friction between two surfaces.
- Friction generally increases with temperature as heat causes expansion and increased roughness of surfaces.

Presence of Lubricants
- Lubricants like oil or grease reduce friction by creating a thin layer between the surfaces, allowing them to slide over each other smoothly.
- Lubricants help in reducing wear and tear of surfaces.

Force of Contact
- The force with which two surfaces are pressed against each other affects the friction between them.
- Greater force of contact leads to higher friction.
In conclusion, friction is a complex force influenced by various factors such as surface roughness, weight of objects, surface material, temperature, presence of lubricants, and force of contact. Understanding these causes of friction can help in managing and reducing friction in different situations.