Final answer:
Newton's second law of motion does not apply under extreme relativistic speeds and when dealing with microscopic objects in the realm of quantum mechanics.
Step-by-step explanation:
Newton's second law of motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
However, there are certain conditions where the second law does not apply. One such condition is when an object is subject to extreme speeds or accelerations close to the speed of light. At such high speeds, relativistic effects come into play and the simple relationship between force, mass, and acceleration described by Newton's second law breaks down.
Another condition where the second law may not apply is when dealing with microscopic objects, such as atoms or subatomic particles. In these cases, quantum mechanics takes precedence over classical mechanics, causing the second law to become less applicable.