Friction is a force that opposes the relative motion or attempted motion between two surfaces in contact. In the case of an oscillatory motion, where there is no direct contact with a surface, friction indirectly affects the motion through other means.
When an object is oscillating, it typically experiences air resistance, which is a form of friction. As the object moves through the air, the air molecules collide with the object's surface, generating a resistive force that opposes its motion. This air resistance gradually dissipates the object's kinetic energy, causing it to eventually come to a stop.
In addition to air resistance, other factors such as electromagnetic forces or damping mechanisms can also contribute to the loss of energy and the stopping of an oscillatory motion. For example, in the case of a pendulum, the oscillations gradually diminish due to the dissipation of energy in the form of heat caused by air resistance, internal friction within the pendulum's pivot, or other damping effects.
It's important to note that while friction plays a role in stopping an oscillatory motion indirectly, it is not the direct cause of the motion's cessation when there is no contact with a surface. The primary factor leading to the decay of oscillations in such cases is the dissipation of energy through various mechanisms.