The discussion centers on the phenomenon of horizontal motion resulting from a vertical stream of water, specifically attributing this to radial pressure differences. Participants illustrate the concept using the analogy of squishy rubber balls that deform upon impact, leading to lateral motion due to pressure exerted during the bounce. The conversation also touches on the atomic interactions that contribute to macroscopic pressure differences, emphasizing the importance of boundary conditions in determining droplet movement.
PREREQUISITESStudents of physics, fluid dynamics researchers, and anyone interested in the mechanics of fluid motion and pressure interactions.
Radial pressure difference.Boltzmann Oscillation 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.Boltzmann Oscillation said:
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?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.
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.Boltzmann Oscillation said:
A.T. said:
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.miltos said: