World of Science - Aerodynamics - Part 3

SECTION 1 - CREATING YOUR OWN REACH IN FISH TANK

This is how you create a 'reach in' fish tank.

Start off with this tank. It is really simple, just a tank with a hole at the side. But with just a hole, air will bubblie in, so let's make the wall penetrate downwards a bit more so that the air will have a harder time bubbling in.

WARNING: Provided the height of water is low enough such that the pressure at the depth of the whole is less than atmospheric pressure. the water will (hopefully) not flow out. However, if the column of water is too high, atmospheric pressure will not be able to support the weight.

Atmospheric pressure is 760 mmHg. Since mercury is 13.5 times denser than water, 1 atmosphere will hold up 10260 mm = 10 metres of water. As long as you conform to that height limit, the tank is safe.
Next you add your fish and plants and stuff inside the tank. Now visitors to your interactive tank will be able to feed your fish and touch your fish.

Warning: Ventilating your tank with an oxygen pump is NOT a good idea. The oxygen will soon displace the water and your fish will be soon swimming in air. Instead, be sure to get someone to design an extremely complicated system for channeling the water out of your tank and aerating it in a chamber independent of the tank, then pumping it back in.

Warning: Do not place exotic fishes in your tank. People might steal them.

And you're done! Probably the worst thing that can happen now would be this.So just make sure that you keep a lookout every now and then.

SECTION 2 - THE BALOONEY EQUATION (sorry I found the common mispronunciation so funny that I just had to put it down)

In a closed system, energy has to be conserved. This basically means that the gravitational potential energy, kinetic energy and pressure exerted perpendicular to the direction of liquid flow is more or less the same.

In other words: Pressure + Density*gravitational acceleration*height+0/5*density *velocity^2 is a constant throughout the system.

Whatever that means, just now that the faster something flows the less pressure it exerts and the lower its height the faster it flows. Makes sense doesn't it? Things go faster as it go downhill.

Just as usual, the lecture was boring.

The demonstrations were just a tad more interesting.


Erm... I guess many of us had seen this many times. Air flows around the ball, causing a region of low pressure around it. When it goes out of balance, the surrounding stationary air with higher pressure pushes it back in.



Atomizer. Water gets sucked up and a cocktail of body fluids and water is sprayed out.


Some burrow design by prairie dogs. Different shape of entrances to allow different flow speeds at different entraces, resulting in a pressure difference that allows ventilation.

I hope the next lesson will be more interesting.

World of Science - Aerodynamics - Part 2

Last Tuesday was a lecture about hydrostatic pressure.

It was really boring. For around 45 minutes the professor tried to explain why pressure throughout a liquid of same depth is constant. I wanted to sleep, but it would seem rude

However, the applications and demonstrations of hydrostatic pressure were rather interesting, yet simple.

1) Land surveying

With a main water tank and pole filled with water connected to the tank with a hose, altitude at which the pole is can be read via markings of the pole. Of course we have to make the water in the tank a lot compared to that in the connecting tube and the pole, so that the change in datum (water level in the tank) is negligible.



2) Hydraulic jack

I always thought that hydraulic jacks were gigantic pieces of equipment controlled by machines, because the great difference between the force humans apply and the weight of the truck is so large, in order to gain sufficient mechanical advantage, one will have to go to the top of the empire state building, hold onto a handle of the same height, and jump off the building in order to lift anything. Turns out that I had the wrong idea. People wouldn't be that stupid. Instead they suck hydraulic liquid from another chamber when needed, so we can push the pump back and forth, drawing liquid and pushing it, instead getting a darwin award.



3) Siphon. Water sucker. Found out about the siphoning effect years ago, but never really thought about how it worked.





4) Magdeburg Water bridge.

As one walk across a conventional bridge, center of mass shifts from one pillar to another. However, in a water bridge, pressure throughout the fluid remains the same, so assuming that there is little turbulence, the force is always evenly spread out across all pillars.

Magdeburg Water bridge

A water bridge in Germany, 918 metres long, the longest aqueduct in whole of Europe. It has been planned for 80 years, but put off after the splitting of East and West Germany. Now, it is used to connect Berlin's inland harbour and ports along the Rhine.



5) Lastly, we were given the task of coming up with a design for a fish tank which allows people to put their hand through a hole at the side to touch the fish. I heard of something like that in Underwater World in Sentosa sometime ago. However I found nothing when I searched the internet. Even went to Yahoo answers, but people gave me useless answers like reach your hand from the top, or have a pump that continuously pumps water back in as it spills out.

Here are some more ideas.

1) Vortex. Vortex tank creates a vortex in front of the opening like a washing machine, so the water does not spill out. Reaching your hand inside might disturb it though, so this 'reach in tank' is a see no touch


2) Plastic gloves. Transparent gloves makes it look as if your hand is reaching in. Gloves are coloured in picture for easier viewing. You can't feed to fish in here, because fish food does not pass through plastic.

Any more ideas on how this might work?