Final answer:
When a non-conservative force acts on an object, it will lose mechanical energy.
Step-by-step explanation:
When a non-conservative force acts on an object, it will lose mechanical energy. Nonconservative forces, such as friction, dissipate the object's mechanical energy as thermal energy, sound, or other forms of energy. For example, when a car is brought to a stop by friction on level ground, it loses kinetic energy, which is dissipated as thermal energy, reducing its mechanical energy.