Things Don't Suck. They Blow.


Ramzy Muliawan link CC BY-SA 3.0 license

It's a hot day and you go out with your friends to get milkshakes. The milkshake arrives, you put a straw in it and then suck up that delicious creamy goodness until you get a brain freeze.

Wrong. Nothing can be sucked because it is simply not a force that is known in nature and I will explain all that in this post.

Solids Can Pull But Fluids Can Only Push

There is a class of materials that are called fluids. Water and other liquids are familiar examples of this but then so are gases such as the air. Lesser known examples of fluids are piles of sand, grain, flour, wood chips and sometimes even boulders (in an avalanche).

Fluids are basically any aggregate material that does not strongly resist permanent deformation and is able to flow.

How Does A Fluid Go Up The Straw?

The key to this question is atmospheric pressure. The surface of the milkshake is subject to 15 pounds per square inch (100 kilopascals for metric types) of pressure from the atmosphere pushing down on it.

When you insert a straw into the milkshake it travels up the tube until it is level with the surface of the milkshake. The surface inside the straw is also subject 15 pounds per square inch of pressure (100 kilopascals) from the atmosphere pushing down on it (we are going to ignore capillary effects for this post).

So the two forces balance each other out and no fluid goes up the straw, that is until you generate a partial vacuum in the straw with your mouth. This partial vacuum reduces the downward forces on the liquid inside the straw but the forces on the surface of the milkshake outside the straw are still there.


Pixnio.com link Public domain image.

Since the pressure outside the straw is greater than the pressure inside the fluid in the straw will get pushed, not pulled, up the straw.

You don't suck, the atmosphere pushes.

Vacuum Cleaners (A Cat's Mortal Enemy)

Vacuum cleaners work in a very similar manner. The motor generates a partial vacuum inside the dirt collection chamber. This means that the pressure outside the vacuum is greater than the pressure inside the vacuum and air is pushed in from outside because of the sudden force imbalance.

If the vacuum is engineered right this will create a miniature tornado in the small spot under the vacuum and dust, dirt, hair and other grossness will get pushed along, not sucked, into the dust collector chamber.

The final dust filter stops it from going through the motor and back out into the room. If the filter ever breaks you will have a bad day (trust me I know).

So the contraption you use to clean your house is not a really a vacuum, it is a only partial vacuum (end pedantic explanation).


NASA link Public domain image.

The Biggest Vacuum Cleaner On Earth

The biggest vacuum cleaners on Earth are called hurricanes in the Atlantic and typhoons in the Pacific.

If a low pressure region forms in some spot over an ocean, then because of Coriolis forces as it moves across the ocean, air will start to revolve around this central low pressure zone. A self-organized structure of air swirling in around a central low pressure zone will form. When the air reaches the centre it will be pushed upwards to higher elevation where it can spill outwards and back to the edges of the storm.

If it is summer and if the surface water is warm then the winds will pick up water vapour from the warm summer ocean and as the vapour rises up in elevation at the centre it cools. As it cools the water vapour condenses out in liquid water and this will release heat.

This released heat causes the surrounding air to warm up and rise even faster which in turn will lower the pressure in the central zone even more. This effect strengthens the hurricane causing faster and faster winds. The air in the central rising column hits high altitudes, stalls out, and is then pushed back out to the edges of the storm (but up above the lower hurricane levels so that the storm structure is not disrupted).

To summarize, we get this kind of giant swirling self-organized structure of a 'partial vacuum' in the centre all powered by the warm surface waters of a summer ocean. The central low pressure zone does not suck air in, the high pressure air on the outside of the hurricane pushes this air in and all of this generates the incredible high speed destructive winds we know as hurricanes.

Fascinating on paper but terrifying in reality.


NASA/Caltech/JPL link CC BY 2.0 license

The Biggest Vacuum Cleaner in the Solar System?

Another vortex phenomenon exists on at least one other planet and that is Jupiter. The Great Red Spot is a massive storm 10,000 miles wide, it is larger than the Earth and it has existed for at least as long as Earth has had telescopes (>400 years).

A bit of searching in to how it works seems to reveal that there is not yet a definitive explanation of how the Great Red Spot works but it seems that it may be primarily due to the different speeds of the cloud bands at different latitudes which are able to generate a large, long-lived vortex.

This is too bad because it looks like the Great Red Spot is not the biggest vacuum cleaner in the solar system (I had high hopes).

The Great Red Spot neither sucks, nor blows, it just swirls.

Closing Words

So now we know that things cannot suck, they can only blow. Vacuums cannot suck matter into them, it requires air from the outside to push air and dust inwards into that low pressure zone in the dirt chamber.

Finally, if you are like me and you think that 'The Last Jedi' sucked you would be wrong, it blew (I even wrote a post on that here about 4 months ago).

Post Sources

https://en.wikipedia.org/wiki/Fluid
https://oceanservice.noaa.gov/facts/hurricane.html
https://en.wikipedia.org/wiki/Tropical_cyclone
https://en.wikipedia.org/wiki/Great_Red_Spot
https://en.wikipedia.org/wiki/Star_Wars%3A_The_Last_Jedi

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That's exactly the reason why it is impossible to stand more than 10 meters above your milkshake and still drink it through a straw. This certainly sucks, but we just have to live with that - at least on earth...:)

Things don't suck and if you are more than 10 m in elevation above your working fluid they don't even blow.

Less catchy but more accurate.

That is so incredibly counterintuitive, I love it! So a vacuum cleaner that creates a full vacuum, would that be a better vacuum cleaner, a worse vacuum cleaner or an you've broken physics vacuum cleaner?

A perfect vacuum cleaner would probably pull the rug up into the dirt chamber, the varnish off of the hardwood floors and the cats out from under the couch.

It could be done but might only have limited industrial uses.

A perfect vacuum cleaner would probably even talk... :D Sorry, I had to add that "feminine touch"... ∜mp

I don’t necessarrily think you will have broken physics, but your vacuum cleaner would have one heck of a bad day as atmospheric pressure would most definitely collapse it. 55 gal. Drums and even some locomotive tanker cars will collapse at a perfect vacuum.

Good to know, thanks!

Great article : )
Creativity & Science blend into a fun to read and educational piece.
Welldone!

Thx, I try to combine humour with scitech to make my posts more enjoyable. It doesn't always work but I do my best.

Reading your article made me realised, it has been 10 years since the last time I studied physics for my A-Level. Great explanation but sadly, I can't relate some of them (due to the fact I've forgotten almost everything :P).

it has been 810 years since the last time I studied physics for my A-Level

Pls tell us all the vitamin stack you take every day. We need to know.

Lol, it's a typo. I meant to write 10 years.

Well I am surprised about this explanation, mainly because I don't remember reading the science behind drinking with a straw :P

Really cool to understand this mate!

Resteemed for the brilliant "wordification" :) ∜mp

Thx, I often use the term 'wordsmithing' to describe the edit and tweaking process in writing.

:) I see; I don't... I like inventing my own words like the "hardonning" thing :D

That is one catchy title :D

Thx, I try to combine humour with scitech to make my posts more enjoyable. It doesn't always work but I do my best.

Hi @procrastilearner!

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Thx for the recognition, it is encouraging.

Very good post and very useful, thanks a lot, regards know me @fauzan93

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