Classical physics is a good approximation to modern physics under certain circumstances. What are they?

Classical physics is a good approximation to modern physics under the following circumstances:

1. Macroscopic Scales: Classical physics is a good approximation when dealing with phenomena at macroscopic scales. This includes objects that are much larger than atoms and molecules, such as cars, planets, and stars.

2. Low Speeds: Classical physics works well for objects moving at speeds much less than the speed of light. As speeds approach the speed of light, relativistic effects become significant and classical physics fails to provide accurate predictions.

3. Low Energy: Classical physics is a good approximation for systems with low energy. When dealing with high energy systems, quantum effects become significant and classical physics is no longer a good approximation.

4. Non-Extreme Conditions: Classical physics is a good approximation when dealing with non-extreme conditions. This means situations that are not at incredibly high temperatures, incredibly high pressures, or incredibly small distances.

In these circumstances, the principles and laws of classical physics, such as Newton's laws of motion or Maxwell's equations for electromagnetism, provide a good approximation of the behavior of physical systems. However, when these conditions are not met, modern physics, including quantum mechanics and relativity, is needed to accurately describe the system.