Forces to crack a pouch after a fall

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    Crack Fall Forces
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Discussion Overview

The discussion revolves around the forces experienced by a pouch (balloon) filled with one liter of water when it falls from a height of one meter and impacts the floor. Participants explore the dynamics of the impact, the forces involved, and the conditions under which the pouch may crack.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the force exerted on the walls of the pouch upon impact, noting that it seems to crack more easily when dropped compared to when a static force is applied.
  • Another participant calculates the gravitational potential energy of the falling pouch as 9.81 J and questions whether this energy translates directly to the force upon impact.
  • Dynamic effects, such as strain rate effects and stress concentrations, are mentioned as factors influencing the balloon's integrity upon impact.
  • A participant reports that during a pressure test, the pouch withstands a force of 2000 N without cracking, raising questions about the pressure exerted by the water on the walls of the pouch and whether this is hydraulic pressure.
  • There is a discussion about the conversion of gravitational potential energy to kinetic energy and the complexities of calculating the impact force due to the non-rigid nature of the balloon and the water inside.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between static and dynamic forces, with no consensus reached on how to quantify the forces involved or the conditions leading to the pouch's cracking.

Contextual Notes

Participants mention various factors affecting the impact, including impulse relationships, deformation of the water, and potential acoustic effects, but these aspects remain unresolved and are not fully quantified.

rah
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Hi

I have a question I need help with.

Im trying to find out how much forces that a pouch (balloon) creates on the inside walls when it hits the floor after a fall.

A pouch (balloon) with one litre of water falls from 1 meter down to the floor.

How much force must the "walls" stand before they crack?

I have tryed to put a known force on top of the pouch and it stands quite a lot.
But when I drop it on the floor it cracks "a lot easier".


R
 
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rah said:
A pouch (balloon) with one litre of water falls from 1 meter down to the floor.

How much force must the "walls" stand before they crack?

I have tryed to put a known force on top of the pouch and it stands quite a lot.
But when I drop it on the floor it cracks "a lot easier".
1 l of water = 1 kg and 1 m, mgh = 1 kg * 9.81 m/s2 * 1 m = 9.81 J.

Does the static force on top of the balloon apply a for equivalent to 9.8 J?


There are dynamic effects and stress concentrations that play a role. When the balloon drops there is a strain rate effect as well as a non-uniformity in the stress field that can cause the balloon material to tear. Some of the stress non-uniformity will arise from friction between the balloon and impact surface, as well as non-uniformity in the wall of the balloon.
 
Thank you for your quick reply.

If I understood you right the force that the balloon hits the floor with is 9,8J or Newton.

The force I use when I pressure test the pouch is 2000N and the pouch doesent have any sign of cracking.

Is it possible to calculate the pressure the water creates on the walls. Is that hydraulic pressure?

R
 
rah said:
Thank you for your quick reply.

If I understood you right the force that the balloon hits the floor with is 9,8J or Newton.

The force I use when I pressure test the pouch is 2000N and the pouch doesent have any sign of cracking.

Is it possible to calculate the pressure the water creates on the walls. Is that hydraulic pressure?

R
When the balloon drops, the gavitational potential energy converts to kinetic energy until the balloon hits the floor (9.8 J). When the balloon hits the floor, the force is determined by the impulse relationship, but it's complicated since the balloon is not rigid. The water deforms as it collapses and the balloon is pushed out sideways (radially) - and there is probably an acoustic/shock wave reverberating through the water.
 

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