Frictional force is the resistance that occurs when two surfaces slide against each other. It acts in the opposite direction of the movement, making it harder for objects to move. This force depends on the types of surfaces in contact and the amount of pressure pressing them together. For example, rubber on asphalt has more friction than ice on metal. There are two main types of friction: static and kinetic. Static friction prevents an object from starting to move, while kinetic friction acts on moving objects. Understanding frictional force is important in various fields, including engineering and physics, as it affects motion and energy efficiency.