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Vortices

Introduction
Public summary: 

Experiments with smoke rings and tornado formation.

Make smoke rings and see how they form
Useful information
Kit List: 

2 Vortex cannons + spares
Polystyrene Cups
Power supply for the smoke generator
Smoke generator
2 Water bottles, food dye and vortex tube connectors for bottles
Canned smoke (for busking/floating)

Packing Away: 

Disassemble vortex cannons carefully.

Frequency of use: 
2
Explanation
Explanation: 

** OVERVIEW ***

This experiment exhibits vortices, in particular in smoke rings. and vorticies in water flowing between 2 bottles.

*** BASIC PROCEDURE AND EXPLANATION ***

This experiment is about smoke rings, but, to understand why they happen, it's best to start with something simple, like pouring water between two bottles. Have you ever noticed what water does when it goes down a plughole? Does it just go straight down? With any luck, your audience will have already noticed that it doesn't, but it's still useful to show them a simple vortex in action using the pair of bottles connected by a plastic connector. The water can't just go straight through (because air needs to go the other way), so it forms a vortex and thus air can go straight up through the middle.

So far the cores of our vortices (whirlpools) have been roughly straight lines. It's possible to make a vortex the core of which bends back on itself in a circle. You can spin your hand in the air at this point - this demonstrates how awkward the thing is to describe without a real example! Fortunately, we have one - since air is a fluid, like water, we can make a ring of vortex in it. If we use smoke, we'll even be able to see it. This is what the smoke machine is for. Using the smoke machine plug in and hit the button, it has around 3 minute warm up time and high output so only switch it on for a couple of seconds. The vortex cannon should show some good smoke rings. You can also feel the force if you fire it at someone, try not to let people get carried away in a fight, this shows we can transmit force through the air. By stacking the polystyrene cups in a pyramid kids can try to knock them over from a set distance. See how far away this can be done, and note how slowly the ring moves. The smoke shows us this travelling. The sides of the hole in the vortex cannon slow down the smokey air near the sides more than that in the middle, and making a twisting movement all of the way round. This makes a ring of vortex - can you see how it's rotating?

You can talk about how the smoke machine works. It pulls in the fluid from the tank and heats it causing it to vaporise and form a cloud. The fluid is a mixture of water and glycol or glycerine. You can then talk along the lines of phases of matter and the transition from liquid to gas. You can talk about why we can see the smoke but the normal gases in the air are transparent. This is because the sheer number of water droplets making up the smoke. Normally light is scattered slightly by gases in the air but because there's not that many molecules we can't really see it. The sheer number in the smoke means it's scattered a lot after only a short distance, hence why we can see it. It's a white colour as it scatters all wavelength equally. It's slightly grey because of some of the absorption from the other parts. (I think this is true at least.)

*** OTHER THINGS TO TALK ABOUT ***

Pipe smokers can make smoke rings, as can volcanos!

vortices in air occur in weather systems. Tornados are a particularly vivid example, but there are big, slow vortices as big as whole countries above us in the sky all of the time, determining the direction of the wind.

Eddy shedding and flag ripples are also interesting (apparently) but I don't know anything about them.

Test with other shaped opening, ring is only stable solution.

Ring is stable, air in centre is moving faster, air at edge slower, this causes a twisting motion, shape is stable as fast air is lower pressure so in relation to stationary air there's a force keeping it in a ring. When it slows the ring expands as the pressure in the ring increases.

If you touch the ring it breaks as its a big disruption to the stability.

You can attempt to get them to interfere and can see some repelling (not sure why it happens though) they can theoretically merge or destroy too but hard to do.

Theres also no net movement of air, think about what this would do to the pressure, air just rotates around the vortex. The smoke is highlighting the forward flow, where we to fill the room with smoke and fire clean air vortices we'd see reversed motion of smokey air.

Risk Assessment
Date risk assesment last checked: 
Tue, 05/02/2019
Risk assesment checked by: 
Josh Garfinkel
Date risk assesment double checked: 
Tue, 05/02/2019
Risk assesment double-checked by: 
Conor Cafolla
Risk Assessment: 

Looking at vortices in shallow water tanks and plugholes, and lemonade bottles. Also, creating smoke rings:

Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Water Spilt water could be a slip hazard 3 3 9 Clear up spills promptly. Make sure the bottles are firmly connected before inverting.
Call a first aider in the case of an injury.
2 3 6
Water Spilt water could be dangerous if there is electrical equipment nearby. 3 4 12 Clear up spills promptly. Isolate electrical equipment from the mains if it may have been affected.
In the event of an accident call a first aider. Switch off power supply to any equipment causing injury.
2 3 6
Canned smoke Canned smoke is flammable. 2 5 10 Ensure it's kept away from naked flames, do not allow the build-up of too much smoke in an unventilated area (e.g. the darkroom tent!).
In case of fire, follow standard procedures for fire (see venue RA). Evacuate area, use fire extinguisher only if safe to do so, call fire brigade.
1 5 5
Smoke machines Smoke machines are hot during operation and can cause burns if touched. 4 3 12 Move using the yoke (hanging bracket) if necessary. Place on a heat resistant surface. Let it cool down periodically.
Call a first aider in the case of an injury.
3 2 6
Smoke Smoke/haze can cause irritation to the lungs and problems for asthmatics. 4 4 16 Minimise time machine is on for. Use in a well-ventilated area. Swap demonstrators on the experiment if required and warn spectators. Avoid breathing in the fumes.
Call a first aider in the case of an injury.
2 4 8
Smoke Excess smoke can affect visibility, increasing the likelihood of other accidents (falls, burns, etc.) 2 4 8 Do not run the machine for extended periods of time. If smoke becomes too thick increase ventilation and cease demonstrating.
Switch off power and call first aider in case of injury. In very poor visibility evacuate as if there were a fire (as per venue RA) opening windows and doors were possible to ventilate area.
1 3 3
Smoke Smoke may set of fire alarms. 4 4 16 Check alarm status of the venue, machine shouldn't produce very hot smoke so heat sensor shouldn't be affected however smoke detectors will be. Consider isolating alarms and the risk of doing so in that venue. Alternatively demonstrate outside.
In the event that the alarm goes off, switch of power and follow standard fire procedure (as per venue RA). Open windows and doors to ventilate area.
2 4 8
This experiment contains mains electrical parts, see separate risk assessment.
This experiment is sometimes run in a darkroom, see separate risk assessment.
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