AMASE: How Do Straws Work?

Posted on Tuesday, April 14th, 2020


[Sound. Guelph University logo and tagline: Improve Life.]

[Cut to Joanne and Mara at the kitchen bar.]

Joanne: On today's episode of Ask Me Anything: Science Edition we tackled this question from Grade 3 student Lucas in Brampton Ontario.

[Cut to Lucas.]

Lucas: I have a question. How do straws work?

[Cut back to Joanne and Mara in the kitchen.]

Mara: Great question Lucas. I've used straws a gazillion times and never really thought about it. How DO they work?

Joanne: That is a good question. So, it's all about pressure. When you push on something like I'm doing on this counter you're creating pressure. So, if I push harder that's more pressure.

Mara: Okay that is true but I don't push on the smoothie to make it go up the straw.

Joanne: That is true, you don't push on the smoothie, but the air in the room does.

Mara: Really? Don't mess with my head!

Joanne: I'm not messing with your head, it's true. So, there's air all around us it's moving around, it's bumping into us and every time it does it exerts a little bit of pressure on us and on the smoothie in the glass. As well as inside the straw. So, the air inside the straw is pushing down on the surface of the liquid and the air in the glass is also pushing down and it balances out.

Mara: So it doesn't move.

Joanne: Well, it doesn't move unless you take the air out of the straw by sucking on it so if you remove the air from the straw there's nothing pushing down on the inside of the straw anymore. The air in the glass is still pushing down and it causes all the liquid to go up into the straw, all the way up to your mouth.

Mara: I bravely volunteer as lead scientist!

Joanne: Perfect I've got just the experiment to do, and you can do it at home as well.

What we've done is we've gone through our cupboards and found a bunch of straws! They're all about the same size opening we have a long one, we have a couple of short ones and we have this crazy-looking one. So, Mara is going to take some smoothie pour it into four different glasses and we're going to time how long it takes her to drink the
smoothie with different straws. We're going to start with the long one. Ready?

[Mara nods.]

Joanne: Let's do this...

[Mara is pouring smoothie into four different glasses.]


[Mara takes the longest straw and drinks the first glass of smoothie.]


Joanne: So that was about 34 seconds. So, now we're gonna try the same amount of smoothie with the short straw. Let's go!

[Mara drinks the smoothie with a short straw.]


Joanne: Okay so that was about 18 seconds with the short straw.

Mara: Makes sense...  less distance to my mouth.

Joanne: That's true plus there's less air in the straw for you to remove in order to create that low-pressure region.

Mara: So, what would happen with two of the short straws?

Joanne: You're gonna try two short straws together? What do you think would happen?

Mara: I think it would be the fastest? Maybe twice as fast? As the short one by itself?

Joanne: All right let's try it! To the smoothie!

[Mara drinks the third glass with two short straws.]

Joanne: Okay you were right! The two short straws together was the fastest time so far, about 12 seconds. One more straw to try. This crazy thing... what do you think is gonna happen?

Mara: I think it's gonna be the longest because of all the wiggles! Longer because the smoothie has further to travel?

Joanne: Alright, let's try it!

[Mara drinks the last smoothie with the long crazy straw.]

Joanne: You were right! The longer the straw, the one with all the turns, took the most amount of time and the two small straws side-by-side took the least amount of time.

Mara: FUN! 

Joanne: That's right fun and this right here [Joanne holds up the short straw], this is a critical piece of technology in the International Space Station.

Mara: This? [Mara takes the short straw.] Really?

Joanne: Absolutely. So, when astronauts are in orbit around Earth liquids don't behave the same as they do on the surface. So, they don't tend to stay in the cup and you can't rely on gravity when you tip it up to your mouth for it to pour in.

Mara: So, they use straws? To create low pressure regions so they can drink?

Joanne: Exactly! And it forces it into their mouth. They have specially designed cups now but for a very long time, if an astronaut wanted something to drink they would have a bag that have the liquid inside that they punched with a straw.

[Cut to image of an astronaut drinking from a straw.]

Mara: Like a juice box!

[Cut back to the kitchen.]

Joanne: Exactly like a juice box. Okay one more thing. Can you think of any animals that use air pressure like this to drink their water?

Mara: Hmmm can I have a hint?

[Sound of elephant]

Mara: Oh an elephant! A cute little elephant!

[Joanne show a drawing of an elephant.]

Joanne: It's true, an elephant! So, an elephant has a trunk and they use it kind of like a straw. 

[Cut to video of elephants in the water drinking.]

Joanne: What they do is they put the trunk in the water and they suck some of the water up into their trunk and then they blow it out of their trunk into their mouth so that they can swallow it.

[Cut back to Joanne and Mara in the kitchen.]

Mara: Like this?

[Mara blows some smoothie out of the straw at Joanne.]

Joanne: I should've seen that coming.

Mara: [Laughing.] Thank you for watching Ask Me Anything: Science Edition! If you have any questions for us just let us know. You want a paper towel?

Joanne: [Nodding.] Please.


In this video, 3M National Teaching Fellowship recipient Dr. Joanne O'Meara and junior scientist Mara explain how straws work!

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