that's funny

should weld spiral fins around the lamp post to make the eddies chaotic and not oscillate between one another

XD lool

Ahahaha! You are awesome 😂

Harvard Natural Sciences Lecture Demonstrations but what is causing the pendulum's frequency? is it the creation of the vortices? if it is then wouldnt it automatically match the frequency of the vortices causing it to be reasonantly excited?

@@changenoways9555 - I think it's more about the material it's made from. Different materials have different atomic structures and characteristics. According to this paper - frequency is the velocity of the sound of this object (if I understood it properly). And you hear daily how different objects and materials sounds - density matters but this is atomic structure. "The resonance frequency of an object is a function of its sound velocity - a material characteristic - as well as of its geometry. " (PDF) Resonance frequency measurements of a few materials for temperature variations. Available from: www.researchgate.net/publication/281549045_Resonance_frequency_measurements_of_a_few_materials_for_temperature_variations [accessed Oct 27 2019].

instablaster

أخي هل لديك معلومات أعمق حول هذا الموضوع وشكرا لك

thank you

@@wolfgangrueckner7151 Hallo Herr Wolfgang! Could you please share the design details of the flow tank?

goo.gl/MMi1XL

badass dude

how are u doing?

Yes the flow rate slows down near the end of the channel because of the transition to the deep reservoir.

It's due to friction. Where the water meets the bottom plate on a micro/nano level, you have to imagine that the surface of the bottom plate is not perfectly flat. Any surface you see around you right now is not perfectly flat. When zoomed in close enough, you will see a mountain like surface. Now where the water molecules meet these mountains at the surface of the bottom plate, you can imagine water molecules getting stuck in between these mountains (in the valleys). We also know that there are certain inter molecular forces between the water molecules. Here we want to focus on the attractive forces. As the molecule that is stuck in between the mountains is pulling on its neighboring molecules, it will slow them down (considering the moving fluid case of this experiment). These molecules will in turn slow down a higher fluid layer as there will be a velocity difference between the layers. So you can imagine that this concatenation of molecules pulling each other back will result in a slower moving fluid eventually. At the start of the ping-pong test, the ball needs to be accelerated first. When the ball is thrown in the water, its initial velocity is zero. The water molecules around the ball are moving fast, as the demonstrator states. The ball also does not have a perfect flat surface. Again the water molecules get stuck in between the mountains of the balls surface. The same pulling motion now causes the water to pull the ball along, as it is not a fixed object (unlike the bottom plate). We know from newtons second law that F=ma, and therefore the pulling force of the water will cause the ball to start moving as the force causes an acceleration a which increases the balls velocity v. After some initial acceleration, the ball will have the same velocity as the fluid. At this point, there will be no resulting pulling force on the ball anymore. So the reason why you can't see the difference in the fluid velocity is because the ball has to accelerate first. Once its velocity is roughly equal to the fluid velocity, the fluid velocity has already decreased due to the bottom plate friction. Hope it helps:)

Some more details about our setup can be found here sciencedemonstrations.fas.harvard.edu/presentations/vortex-shedding

Yes I'm aware this is old.

Yes.

el tigre.

Yes when the vortices are shed at a frequency that corresponds to the natural frequency of the physical pendulum, the amplitude becomes large. The situation is analogous to pushing someone on a swing: when you push at the right intervals, the person on the swing will travel the maximum distance between pushes. The natural frequency of the physical pendulum is set by its length, relative to the pivot (e.g. a longer length gives a slower frequency, a shorter length gives a faster one). When the end of the pendulum is in the water, the natural frequency will slow down a little bit, due to the drag force of the water.

+ian prakoso You can find references for further study cited in our writeup sciencedemonstrations.fas.harvard.edu/presentations/vortex-shedding

Kenneth Boyd Interesting question. The knuckleball definitely deviates from a normal trajectory due to variations in pressure. There can be several factors that lead to these variations (local turbulence, temperature variations, etc). But I would imagine that vortex shedding could plausibly play a role.

The vortices cause the surface of the water to no longer be perfectly flat, and so refraction at the air-water interface can bend light away and cause shadows at the bottom of the tank.

@@NatSciDemos Thanks !

The socks diffuse the water flow to minimize a strong directed stream.

Thank you for sharing 🙏🏻✊🏻❤️