Why stream of water sent in upward direction spread like fountain?

In summary: This is because water is pretty much incompressible. In summary, when a stream of water is blown in an upward direction, it eventually loses energy and momentum causing it to stop. Gravity is still acting, so the water cannot go up or down, and it cannot go in because it would run into itself. Therefore, the only way it can go is out, resulting in the water spreading like a fountain. This is due to the conservation of energy and mass. The exact solution for this phenomenon is complex and cannot be obtained analytically.
  • #1
vkash
318
1
why stream of water blown in upward direction spread like a fountain. I failed to explain it can you please help.

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  • #2
As it goes up, it loses energy and momentum, so eventually it has to stop. When that happens, it has to go somewhere since gravity is still acting. It can't go up because it has no more kinetic energy. It can't go down because the rising column of water is in the way. It can't go in because it would run into itself. Therefore, the only way it can go is out.
 
  • #3
boneh3ad said:
As it goes up, it loses energy and momentum, so eventually it has to stop. When that happens, it has to go somewhere since gravity is still acting. It can't go up because it has no more kinetic energy. It can't go down because the rising column of water is in the way. It can't go in because it would run into itself. Therefore, the only way it can go is out.

So according to your explanation water will spread after becoming it's kinetic energy zero.
 
  • #4
It's not important that the kinetic energy is near zero. You can point a stream of water at an upward angle, so the water maintains some horizontal motion, but it still spreads out. This is because water is pretty much incompressible. If the stream slows down, it needs to get wider to conserve volume.
 
  • #5
vkash said:
why stream of water blown in upward direction spread like a fountain. I failed to explain it can you please help.

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I thought this was a silly question, but there are some nice simple results, based on jets that point downward.

For the simple case, neglect viscosity and surface tension, and assume the exit velocity of the jet is uniform across the cross-section. Then you use Bernoulli's law (conservation of energy), written as [itex]\frac{1}{2} \rho U^{2}_{0}=\frac{1}{2} \rho U^{2}_{\infty}-\rho gz[/itex] and conservation of mass [itex]U_{0} R^{2}_{0} = U_{∞} R^{2}_{∞}[/itex] to get:

[itex] R(z) = R_{0}(1-\frac{2gz}{U^{2}_{0}})^{-1/4}[/itex]

Which is sort of symmetric to the drawing down of a dropping jet. Adding a parabolic velocity profile at the exit (Poiseuille flow), viscosity effects, and surface tension complicate the solution considerably. The solution above can be written in terms of the Reynolds number and Froude number as well.

It is claimed that an exact analytic solution of jet draw-down cannot be obtained (Middleman, "modeling axisymmetric flows"), and I suspect the upward-directed jet has the same problems.
 
  • #6
Khashishi said:
It's not important that the kinetic energy is near zero. You can point a stream of water at an upward angle, so the water maintains some horizontal motion, but it still spreads out. This is because water is pretty much incompressible. If the stream slows down, it needs to get wider to conserve volume.

It doesn't matter that the kinetic energy is beig lost while moving up? Why do you suppose the water slows down an therefore widens then?

It is losing energy, aka slowing down. They are one and the same.
 
  • #7
It doesn't matter that the kinetic energy is beig lost while moving up? Why do you suppose the water slows down an therefore widens then?

It is losing energy, aka slowing down. They are one and the same.

Kashishi was agreeing with you, but pointing out that the kinetic energy could still be greater than zero. The water will spread out as it loses KE and slows, but it may still have a lot of KE.
 

1. Why does a stream of water sent in an upward direction spread like a fountain?

When a stream of water is sent in an upward direction, it is being propelled by a force. As the water rises and falls, it breaks into droplets due to the force of gravity. These droplets then spread out in a circular pattern, creating the appearance of a fountain.

2. What causes the stream of water to break into droplets?

The force of gravity causes the stream of water to break into droplets. As the water rises and falls, it experiences changes in velocity and direction, which causes it to break apart into smaller droplets.

3. Can the height of the stream of water affect the spread of the fountain?

Yes, the height of the stream of water can affect the spread of the fountain. The higher the stream of water, the longer it has to fall and break into droplets, resulting in a wider spread of the fountain.

4. Are there other factors that can affect the spread of the fountain?

Yes, there are other factors that can affect the spread of the fountain, such as the force of the initial stream of water, the viscosity of the water, and any obstacles or barriers that may disrupt the flow.

5. Can this phenomenon be observed with other liquids besides water?

Yes, this phenomenon can be observed with other liquids besides water. Any liquid that can be propelled by a force and is affected by gravity can exhibit a similar behavior, such as oil or soda.

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