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My confusion is: according to Newton's first law, an object will remain at rest or at a constant velocity when the net force acting on it is zero. However, in the mass-string system, the mass remained at rest despite the fact that the downward force exerted on the mass, in turn, on the top string exceeds the maximum tension that the string can withstand (as it caused the second string to break). So does this imply that not all the force applied on the bottom string are exerted on the mass (as the tension in the top string is lower than the bottom one)? If so, where did the force go? And why is that when the force is exerted over a longer period of time this disparity between the force applied and the force experienced by the top string seems to vanish?
Essentially, why is the tension in the top string smaller than the bottom one when jerked quickly?
I did some research online and came across answers similar to this one: "By pulling the string slowly, we are putting a strain in the string below and above the weight. Due to the mass of the weight, the strain above the weight is much larger than below. The string snaps wherever the strain is the highest. When a sharp jerk is exerted on the string, the inertia of the weight keeps the strain below the weight. Although there is some strain above the weight, compared to the strain below the weight the strain in the latter is still higher, and the string snaps below the weight."
I understand that it has something to do with inertia, but how exactly does inertia "keeps the strain below the weight"? Please explain with details.
This is my first post, thanks for any help I can get!