When a system loses its motion due to friction between two surfaces, the kinetic energy of the system is ultimately converted into other forms of energy, typically thermal energy or heat. Friction is a force that opposes the motion of objects in contact, and it arises from the interaction between the atoms or molecules at the surfaces of the objects.
As the objects move against each other, the frictional force acts in the direction opposite to the motion, gradually slowing down and eventually stopping the objects. This force does negative work on the system, meaning it removes energy from the system.
The kinetic energy of the system is given by the equation: K = (1/2)mv^2, where m is the mass of the object and v is its velocity. As the objects experience friction, the work done by the frictional force reduces the system's kinetic energy. This work is equal to the force of friction multiplied by the distance over which it acts.
As the objects slow down, the kinetic energy decreases, and the energy is converted into heat. The friction between the surfaces causes microscopic interactions between the atoms or molecules, leading to an increase in their kinetic energy, which manifests as an increase in temperature. This conversion of kinetic energy into thermal energy is due to the random motions and vibrations of the particles involved.
In summary, when a system loses its motion due to friction, the kinetic energy is transformed into thermal energy or heat through the work done by the frictional force.