Does it take two forces to deform an object?

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The discussion centers on whether two forces are needed to deform an object, particularly in the context of space junk impacts. It argues that a single force from the impacting object can cause deformation, with the second force being the reaction of the object being hit, represented by its mass and acceleration. The concept of inertia is highlighted, especially in high-speed impacts where the effects are localized. Space junk travels at significantly high velocities, leading to rapid impacts that primarily affect the immediate area. Overall, the conversation emphasizes that deformation can occur from a single force under specific conditions, particularly during high-rate processes.
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I have a question - if 2 forces are required to deform an object then why does a piece of space junk impacting an object in space cause deformation? What is the second force?
 
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Who says it takes two (external) forces to deform an object? Just look at a slow-motion video of bat hitting a ball.
 
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Action and Reaction ?? :wink:
 
Ignoring the subtleties, inertia becomes dominant for high rate processes.
 
tomR said:
What is the second force?
Because ##F = ma##.
The first force is ##F##, the force applied by the impacting object.
The second force is ##ma##, or the mass of the object being hit multiplied by the acceleration of that object.

Frabjous said:
inertia becomes dominant for high rate processes.
Typical space junk is moving roughly ten times the velocity of a high velocity rifle bullet. That's a high rate process. The whole impact happens so fast that only the material in the immediate vicinity of the impact is affected. Space junk impact is finished punching a hole (or crater) before the material away from the impact is affected by the impact force.
 
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