How much time does it take to the floor to stop a falling book?

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    Book Falling Time
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Discussion Overview

The discussion revolves around the dynamics of a falling book and the time it takes for the floor to stop it upon impact. Participants explore various factors influencing the stopping time, the normal force exerted by the floor, and the deceleration experienced by the book, considering different materials and conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions how long it takes for the floor to stop a falling book and how far the book penetrates the floor, suggesting that various parameters affect the outcome.
  • Another participant notes that the material of the floor and the book will influence the stopping time, with concrete providing a quicker stop than carpet.
  • A participant speculates that if the normal force exceeds gravitational force, the book might bounce, introducing the idea that floor density is a relevant factor.
  • One participant provides a model indicating that a rectangular block could experience deceleration forces ranging from 100G to 10,000G, depending on the materials involved, and estimates stopping times in milliseconds to microseconds.
  • Another participant expresses skepticism about the high deceleration values, seeking clarification on the direction of the deceleration force and acknowledging their limited understanding.
  • Some participants express curiosity about specific properties or relationships that could define the complete stopping time of a falling object, noting that the final velocity would not be zero.
  • Examples of drop-testing scenarios are provided to illustrate high deceleration forces, with references to missile testing and shock-testing of electronic devices.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact stopping time or the factors influencing it, with multiple competing views and uncertainties remaining regarding the dynamics of the impact.

Contextual Notes

The discussion highlights the dependence on various assumptions, such as the properties of the materials involved and the initial conditions of the drop, which remain unresolved.

Mad_Eye
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sorry if the title is not clear, if you have a better idea i'll change it.

say i drop a 10kg book to the floor. when it reach the floor, the floor stops it by "activating" the Normal force on it...
my question is, how much time does it take to the floor to stop the book, and by this time how far does it get into the floor... and what's the magnitude of the normal force regarding those...
obviously that's probably depends on a lot of parameters but just try to give me an approximate answer with average parameters to the floor, the book, and everything else


if don't get it right just tell me..
 
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Thats going to depend on the makeup of the floor and the book. If you drop it on concrete it will stop faster than it will on carpet.
 
I'm somewhat assuming here... But if the book WOULD have a higher normal force than gravity then wouldn't it bounce for a short time? I'm a level 3 physics student, so I'm just taking a stab in the dark here... And of course the density of the floor would be a factor
 
If you replace the book with a rectangular block (so you don't have to think about what happens to the individual pages if the book lands on its edge) and it landed flat on one face, the deceleration of the block would typically be in the range of 100G up to maybe 10,000G, depending on the materials of the block and the floor.

A typical deceleration used for modelling this type of impact is 3000G.

So if the block velocity was say 10 m/s before impact, the stopping time would be of the order of a few milliseconds, down to microseconds.

The large forces produced by the large decelerations explain why things break when you drop them, of course.
 
So the deceleration force is downward? I can see how it makes sense, objects come to an abrupt stop usually, but it seems crazy that it would decelerate at 3000G, or close to 10 000 m/s2? Sorry my understanding of this is minimal
 
mburt said:
So the deceleration force is downward? I can see how it makes sense, objects come to an abrupt stop usually, but it seems crazy that it would decelerate at 3000G, or close to 10 000 m/s2? Sorry my understanding of this is minimal

It depends on the velocity and the makeup of the floor and the falling object.
 
I think common sense could tell you that, but I'm wondering if there's a specific property or relationship which deals with the complete "stop" time of a falling object. The V2y of the object wouldn't be zero though, so I'm not sure really what could be used
 
mburt said:
I think common sense could tell you that, but I'm wondering if there's a specific property or relationship which deals with the complete "stop" time of a falling object. The V2y of the object wouldn't be zero though, so I'm not sure really what could be used

Hrmm. I'm sure there is, but I don't know the math behind it all.
 
mburt said:
So the deceleration force is downward? I can see how it makes sense, objects come to an abrupt stop usually, but it seems crazy that it would decelerate at 3000G, or close to 10 000 m/s2? Sorry my understanding of this is minimal

Here are a couple of examples that might convince you (randomly picked by Google).

Drop-testing of missiles, as a cheap way to produce the same accelerations as firing the missiles from a gun - about 20,000G. http://www.empf.org/empfasis/2010/September10/tech-tips-910.html

A company that does shock-testing of electronic circuit boards for cellphones, laptops, etc using, with a test machine that can produce accelerations of 5000G. http://www.dfrsolutions.com/drop-testing/

For comparison, assume about the pistons in your car engine are doing simple harmonic motion with a stroke of 0.1m at 6000 RPM (100 rev/sec). The acceleration =
0.05 x (2 pi x 100)^2 = about 20,000 m/s^2 = about 2000G.
 
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