Collisions Problem: Finding Gs During Impact

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Discussion Overview

The discussion revolves around calculating the g-forces experienced by an object, specifically a TI-89 graphing calculator, when dropped from a height and impacting a hard surface. Participants explore the factors affecting the impact, including the time of collision and material properties, while considering both theoretical and experimental approaches.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks information on the time duration of the collision to calculate g-forces after dropping an object.
  • Another participant suggests finding the acceleration during impact and dividing it by the acceleration due to gravity to determine g-force.
  • A participant emphasizes the need for the time of impact deformation, which is influenced by the materials involved.
  • It is proposed that finite element modeling could be used for theoretical calculations, but experimental measurement is likely necessary for accuracy.
  • One participant mentions their interest in the tolerance required for accelerometers, noting they are rated for 3500g and questioning how much to account for in testing.
  • Another participant provides context by stating that typical drop tests for laptops result in accelerations around 200g.

Areas of Agreement / Disagreement

Participants express varying views on the methods to determine the impact forces, with some advocating for theoretical modeling and others for experimental measurement. There is no consensus on the specific time of impact or the necessary tolerances for accelerometers.

Contextual Notes

The discussion highlights the complexity of measuring impact forces, including the dependence on material properties and the need for experimental validation. Assumptions regarding the deformation characteristics of the materials involved are not fully explored.

Who May Find This Useful

This discussion may be useful for individuals interested in impact physics, engineering applications involving drop tests, or those working with accelerometers in experimental settings.

tonytnnt
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Hi, I'm trying to figure out the number of g's something undergoes after being dropped and hitting the floor. So far I've figured out that I need the time it takes for the collision to occur. I know it's not instantaneous, but I can't find any information on it, so can you point me in the right direction? Are there tables with this information available?

P.S. If you need a scenario to figure out what I'm talking about (since I'm not sure if I've worded it correctly) if I were to drop my TI-89 graphing calculator from a height of about 2 meters, it should reach about 6.3 m/s in a vacuum. I need to figure out how many g's the calculator would experience when hitting a concrete floor (or slate or marble etc.)
 
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All you need to do is find that acceleration (m/s2). To get the g-force, just divide that by the acceleration due to gravity.
 
Yeah I know I need to find the acceleration. I have the velocity, but I need the time it takes for the impact deformation to occur when the plastic (or some other material) hits the concrete.
 
It depends on the structure and rate of deformation of the thing and the floor. It is just about possible to model this using finite element programs but for an accurate answer you pretty much have to measure it experimentally.
In fact it is usually easier to measure the acceleration with embedded accelerometers and calculate the time.
 
Actually I'm trying to figure out what kind of tolerance I need for accelerometers :-P The ones I want to use are rated for 3500g max, but I'm not sure how much I should account for. Oh, well. Trial and error I suppose.
 
I think 3500g is up in artillery round accelaration.
Typical 2-3 foot drop tests for laptops are around 200g.
 
thanks, looks like I might need to do some testing.
 

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