Altitude needed to create an impact of 4kg using a weight of 70g?

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Discussion Overview

The discussion revolves around determining the altitude required to create a specific impact force using a 70g weight dropped in a vacuum under Earth's gravity, aiming for an impact equivalent to 4kg. The conversation touches on concepts of kinetic energy, momentum, and the complexities involved in measuring impact forces.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the phrasing of "an impact of 4kg," suggesting it should refer to a force of 40N, which is the gravitational force on a 4kg mass.
  • Another participant emphasizes that the required altitude is indeterminate and depends on the rigidity of both the object being dropped and the target surface.
  • A calculation is presented indicating that to achieve a force of 40N, the deceleration rate would need to be approximately 571 m/s², which is significantly higher than Earth's gravity.
  • It is noted that for rigid objects, such high acceleration could be achieved from a very short drop, while for less rigid objects, a greater height would be necessary.
  • One participant mentions that predicting impact force is complex due to numerous influencing factors, suggesting that momentum and energy transfer are more reliable parameters to consider.

Areas of Agreement / Disagreement

Participants express differing views on how to approach the problem, with no consensus on a specific altitude or method to calculate the required height for the desired impact force. The discussion remains unresolved regarding the exact parameters needed.

Contextual Notes

The discussion highlights limitations in predicting impact forces due to the dependence on material properties and the complexities of real-world conditions, which are not uniform.

conordee
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Would anyone know what altitude would be needed within a vacuum in Earth's gravity to create an impact of 4kg using a weight of 70g? Thanks
 
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That depends on the impact. The height (together with gravity and your weight) determines kinetic energy and momentum, but the magnitude of deceleration depends on the length of this deceleration.

In addition, it is not a good practice to talk about "an impact of 4kg". I think you mean the force of 40N (Newton), which is the gravitational force a mass of 4k feels on earth.
 
please excuse my bad wording, but I hope you can under stand what I am getting at. Say if i was to create a large tube (with a vacuum) 400ft in the air, on Earth of course. And i dropped a 70g weight from the top, what height? would i need the tube so that the force when the weight hit the bottom would be equal to 4kg?
 
As has already been pointed out, the answer is indeterminate. It depends on the rigidity of the object you are dropping and the rigidity of the target onto which it is dropped.

In order for a 70g object to produce a force of 40 Newtons would require a decelleration rate of 40N / .070kg = 571 meters/second/second ~= 57 times the acceleration of gravity.

For sufficiently rigid objects, that acceleration could be attained after a drop of less then 1cm. For sufficiently fluffy objects, it would obviously take much farther.


One crude estimate would be to compare the deflection at impact to the height of the drop. You need the height of the drop to be roughly 57 times the deflection at impact, all things being equal.

[ But in the real world, all things are never equal ]
 
Just to expand on this a little, force of the impact is rarely a parameter you deal with. It can be important, but it's also nearly impossible to predict. Way too many factors go into it. What you can determine for a particular impact are momentum and energy transfer. Momentum is measured in kg*m/s or, equivalently, in N*s. Energy is in Joules. If you know both, you can say a lot about the impact.
 
Ok I get it now, thanks
 

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