How does a the vertical force of gravity end in horizontal motion?

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Discussion Overview

The discussion revolves around the mechanics of how vertical forces, specifically gravity, can lead to horizontal motion in a stream of water. Participants explore concepts related to pressure differences and the behavior of water upon impact with a surface, examining both macroscopic and atomic perspectives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the force causing horizontal dispersion of water upon impact, seeking references.
  • Another participant suggests that radial pressure difference is the force responsible for this horizontal motion.
  • A visual analogy involving squishy rubber balls is presented to illustrate how deformation during impact can lead to horizontal movement.
  • A participant expresses confusion about the application of radial pressure in physics, questioning its relevance to water and atomic interactions.
  • It is proposed that on an atomic level, bouncing occurs, while macroscopic behavior is described using the concept of pressure.
  • A clarification is made regarding the terminology, suggesting the use of "radial external pressure differences" to describe the phenomenon.
  • One participant points out that the original question pertains to a stream of water rather than a droplet, emphasizing the focus on initial horizontal acceleration.
  • A later reply acknowledges the oversight regarding the distinction between a stream and a droplet, suggesting it is a variant of the same question.

Areas of Agreement / Disagreement

Participants express differing views on the specifics of the forces at play and the relevance of concepts like radial pressure in the context of the original question. The discussion remains unresolved regarding the precise mechanics involved in the transition from vertical to horizontal motion.

Contextual Notes

There are limitations in the discussion regarding the definitions of terms like radial pressure and the boundary conditions affecting water motion. The distinction between a stream of water and a droplet is also noted but not fully explored.

Boltzman Oscillation
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When a stream of water falls perfectly vertical, some water hitting the surface will disperse horizontally. What is the force that causes this? References would be awesome!
 
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Boltzmann Oscillation said:
What is the force that causes this?
Radial pressure difference.
 
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Boltzmann Oscillation said:
some water hitting the surface will disperse horizontally. What is the force that causes this?
To help you see why the reply by @A.T. is correct, you can picture two squishy rubber balls, dropped side-by-side touching each other. When they impact the ground at the same time, they both deform during the bounce and bulge outward on the sides. This causes the two balls to push on each other during the bounce, causing them to bounce apart instead of straight back up.

:smile:
 
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berkeman said:
To help you see why the reply by @A.T. is correct, you can picture two squishy rubber balls, dropped side-by-side touching each other. When they impact the ground at the same time, they both deform during the bounce and bulge outward on the sides. This causes the two balls to push on each other during the bounce, causing them to bounce apart instead of straight back up.

:smile:
Wow that really helped me understand the concept. Now when I searched for radial pressure, I only found engineering topics. Is radial pressure not encountered in a physics curriculum? How would this apply to water? Do the individual atoms bounce apart from each other too?
 
Boltzmann Oscillation said:
Do the individual atoms bounce apart from each other too?
On the atomic level that's what happens. On the macroscopic level we use the concept of pressure which is the average result of all this bouncing.
 
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A.T. said:
Radial pressure difference.

I would prefer to express it as Radial external pressure differences.

In other words, among others, It is the boundary conditions that determine the movement of the droplet, or of the parts of it.
 
miltos said:
It is the boundary conditions that determine the movement of the droplet, or of the parts of it.
The OP asks about a stream of water, not a droplet. The question is, as far I can see, about the initial horizontal acceleration of the water, not about droplet formation.
 
Ohhh, i didn't noticed that.
I any case, it is just a variant of the same question.
 

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