Sample DE & Write-up

Funny Funnel

If you have tried transferring a liquid into a bottle through a funnel, you may have noticed that you have to lift the funnel from time to time when the liquid collects in the funnel and does not flow down. Try it at home. It doesn’t always do that but some times it does.

The question is: why does it do that?

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An alternative analysis is provided below to show you that there isn’t necessarily just ONE single correct wording for a solution.

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Humpty Dumpty
Mr Gurung
Science M4/5
Date

Funny Funnel

The Problem
Funnels are used when transferring a liquid substance from one container to another with especially small openings such as a bottle.  When the liquid is poured into the funnel however, invariably, it has to be lifted from time to time in order to facilitate the flow of liquid into the bottle, otherwise the water collects in the funnel. Why does the liquid collect on the funnel instead of flowing into the bottle continuously and smoothly?

The Solution
Empty containers that appear to contain nothing, actually contains air.  The air inside an open container is at atmospheric pressure.  Should the container be filled with some other thing or object, then the air is replaced by it.  In the process of displacing the air inside the container, generally the air escapes into the atmosphere through one or more openings or outlets in the container.  However, if there is no opening, then the object cannot displace the air inside.  Not only that, with nowhere to go, the air inside may even get compressed, increasing the pressure it exerts, as more and more of the thing is piled over it.

What happens to the liquid over the funnel in the above instance is exactly that.  The empty bottle contains air.  As the mouth of the bottle is the only outlet, which now is covered with a funnel.  And as such, when a liquid is poured in the funnel, the air must also escape through the funnel itself.  But when liquid is quickly poured into the funnel, the outlet is completely sealed by the liquid.  The trapped air inside is slightly compressed exerting a bigger pressure on the container, the funnel and the liquid in the funnel than the pressure they experience from the air outside, and thus holding up the liquid in the funnel.  Lifting the funnel then provides an outlet for air to escape from other than through the funnel itself enabling the liquid to flow into the bottle.

So, the reason the liquid does not flow and collects in the funnel is because of the trapped, compressed air inside the bottle, unable to escape, exerting a much bigger than atmospheric pressure on the liquid in the funnel holding it up.

This of course does not occur all the time.  Two factors affect this. Firstly, the size of the funnel: the smaller the funnel, the more readily and frequently does this occur.  Secondly, how fast the liquid is poured: the faster the liquid is poured, the more readily and frequently this occur.

 

[You could have included a schematic diagram illustrating the process.]

[If you received help you must in-text reference the materials and cite it here.]

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Obviously, there isn’t just one single way of writing a solution to a discrepant event. Here’s another analysis, worded slightly differently.

Alternative analysis (first part of the Solution):

Empty containers that appear to contain nothing, actually contains air.  The air inside an open container is at atmospheric pressure.  Should the container be filled with some other thing or object, then the air is replaced by it.  In the process of displacing the air inside the container, generally the air escapes into the atmosphere through one or more openings or outlets in the container.  However, if there is no opening, then the object cannot displace the air inside.  Not only that, with nowhere to go, the air inside may even get compressed, increasing the pressure it exerts, as more and more of the thing is piled over it. When a liquid is poured into the container, it flows into it under the influence of gravity. But should the air pressure built inside reach a value bigger than that exerted by the fluid, then upthrust will prevent the liquid from freely flowing into the container.

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