# What is zero gravity?

An episode of [Science for Kids / Science's Not Boring: The Kids Science Podcast](https://invisiblenetwork.ai/podcast/1896928296), 15 Jun 2026, 14 min.

Audio: https://www.buzzsprout.com/2624612/episodes/19348109-what-is-zero-gravity.mp3

Imagine living on the International Space Station, zooming around the Earth at a mind-blowing 17,500 miles per hour! But what actually happens to your human body when there is absolutely no gravity holding you down? Hosts Mira and Finn are blasting off to explore the wild, weird, and wonderful effects of microgravity! Did you know that if you went to space right now, you would instantly grow up to two whole inches taller? Without gravity to squish your spine, you stretch right out! But that is just the beginning. You'll also learn about "puffy-face, bird-leg syndrome," why astronauts have to cover their food in spicy hot sauce just to taste it, and why drinking water involves catching giant, wobbly floating blobs! Discover why astronauts must strap themselves to the walls like bats just to get a good night's sleep, and why they have to run on special bungee-cord treadmills for two hours every single day. Get ready to learn the amazing science behind how the human body adapts to life in the stars!

## Transcript

[0:46] SPEAKER_00: Welcome to Science Is Not Boring by Kidopoly.com.
[0:49] SPEAKER_00: I'm Mira! And I'm Finn.
[0:52] SPEAKER_00: Whenever there is a really clear night, I bet lots of us love going outside to do some stargazing.
[0:58] SPEAKER_00: Have you been looking at the sky, Finn?
[1:01] SPEAKER_01: Oh, I love looking at the stars.
[1:03] SPEAKER_01: Especially when the sky is super clear and you can see the shooting stars.
[1:08] SPEAKER_01: It makes me wonder what it's like way up there.
[1:11] SPEAKER_00: Same! But staring up at the giant blackness of space made me wonder, what would actually happen to your human body if you travelled up there?
[1:21] SPEAKER_01: Like, if I was an astronaut.
[1:24] SPEAKER_01: That sounds kind of intense.
[1:26] SPEAKER_00: Exactly! Get ready for this.
[1:28] SPEAKER_00: If you went to space right now, you would instantly grow taller.
[1:32] SPEAKER_00: In fact, you could grow as much as two whole inches or five centimetres taller.
[1:38] SPEAKER_01: Wait, really?
[1:40] SPEAKER_01: Just by going to space?
[1:42] SPEAKER_01: Do I get to keep the extra height when I come home?
[1:45] SPEAKER_00: Well, you will have to wait and see.
[1:48] SPEAKER_00: Today we are talking about the wild, weird, and wonderful things that happen to a human body when you take away gravity.
[1:55] SPEAKER_01: Okay, I am so ready for this.
[1:58] SPEAKER_01: But I am definitely staying firmly on the ground for now.
[2:01] SPEAKER_01: Let's hear it.
[2:02] SPEAKER_00: Okay, so let's set the scene.
[2:05] SPEAKER_00: Imagine you are living on the International Space Station, or the ISS.
[2:10] SPEAKER_00: Where exactly is that?
[2:12] SPEAKER_00: Is it near the Moon?
[2:14] SPEAKER_00: Actually, it is much closer.
[2:16] SPEAKER_00: It's a giant floating laboratory, about the size of an entire American football field, orbiting Earth at an average altitude of 250 miles.
[2:27] SPEAKER_00: That's 400 kilometres straight up in the sky.
[2:30] SPEAKER_01: Whoa, that's really high.
[2:33] SPEAKER_01: Is it moving fast?
[2:34] SPEAKER_00: Oh, it is flying.
[2:36] SPEAKER_00: The ISS travels at a mind-blowing 17,500 miles per hour.
[2:43] SPEAKER_00: That is 28,000 kilometres per hour.
[2:47] SPEAKER_01: No way! That is faster than a speeding bullet.
[2:50] SPEAKER_00: Yes, way.
[2:52] SPEAKER_00: At that incredible speed, the space station circles the entire Earth every 90 minutes.
[2:58] SPEAKER_00: That means astronauts up there get to see 16 sunrises and 16 sunsets every single day.
[3:05] SPEAKER_01: That is so fast.
[3:07] SPEAKER_01: But wait, if it is moving that fast, why aren't the astronauts pushed super hard against the walls, like on a fast roller coaster?
[3:15] SPEAKER_00: Because the space station and everything inside it are in a constant state of freefall toward Earth, but moving sideways fast enough to continuously miss the planet.
[3:26] SPEAKER_00: This creates a microgravity environment.
[3:28] SPEAKER_00: Basically, they are completely weightless.
[3:31] SPEAKER_00: So there is no up and no down?
[3:34] SPEAKER_00: Nope.
[3:35] SPEAKER_00: Gravity is the invisible pull that keeps our feet on the ground here on Earth.
[3:40] SPEAKER_00: But up there, that downward pull is basically gone.
[3:43] SPEAKER_00: And that causes some totally weird things to happen to the human body.
[3:48] SPEAKER_00: Like the growing taller thing?
[3:50] SPEAKER_00: We'll get to that.
[3:51] SPEAKER_00: But first, what do you think happens to all the blood and water inside you when gravity turns off?
[3:58] SPEAKER_00: Um does it just swish around in my stomach?
[4:02] SPEAKER_00: Actually, yes, a little bit.
[4:05] SPEAKER_00: On Earth, gravity is constantly pulling your blood and bodily fluids down toward your legs.
[4:11] SPEAKER_00: But in space, there's no gravity pulling down.
[4:14] SPEAKER_00: So where does all that fluid go?
[4:17] SPEAKER_00: It goes up, into your chest and head.
[4:21] SPEAKER_00: Scientists call this the cephalic fluid shift.
[4:24] SPEAKER_00: Up to two whole litres of fluid, which is like a giant soda bottle, moves from the lower body into the upper body.
[4:33] SPEAKER_01: Two litres?
[4:34] SPEAKER_01: That's a huge amount of liquid just moving into your face.
[4:38] SPEAKER_00: Does it look weird?
[4:39] SPEAKER_00: It does! NASA astronauts jokingly call it the puffy face bird leg syndrome, because all the fluid leaves their legs, making them super skinny like a bird, and their faces get totally puffy and round.
[4:54] unknown: Hahaha!
[4:55] SPEAKER_00: Bird legs! Does the puffy face hurt?
[4:58] SPEAKER_00: Not really, but it makes them feel like they have a terrible head cold.
[5:02] SPEAKER_00: The extra fluid causes their nasal passages to swell, so their noses get all stuffy.
[5:08] SPEAKER_00: And because of that, they can't smell or taste their food very well.
[5:13] SPEAKER_01: Oh no, space food already sounds kind of weird.
[5:16] SPEAKER_01: How do they fix it so they can taste anything?
[5:19] SPEAKER_00: They use tons of hot sauce.
[5:21] SPEAKER_00: Astronauts request intense condiments like sriracha, spicy mustard, and horseradish, just to get a little bit of flavour.
[5:30] SPEAKER_01: Wow, what about drinking water?
[5:32] SPEAKER_01: Does water act weird in zero gravity too?
[5:36] SPEAKER_00: It acts completely wild.
[5:38] SPEAKER_00: Without gravity, water doesn't pour.
[5:41] SPEAKER_00: It forms giant wobbly blobs floating in the air, held together by an invisible force called surface tension.
[5:49] SPEAKER_01: So if you cry because your food is too spicy, do the tears just float away?
[5:54] SPEAKER_00: Actually, tears stick to your face in a big watery blob right over your eyes.
[5:59] SPEAKER_00: To drink, astronauts have to suck liquid out of special foil pouches, using long straws with clamps so the water doesn't float away.
[6:09] SPEAKER_01: Okay, puffy faces and floating blobs of water.
[6:12] SPEAKER_01: But you promise to explain the growing taller part.
[6:15] SPEAKER_01: I want to know how that works.
[6:17] SPEAKER_00: Right, so feel the middle of your back.
[6:21] SPEAKER_00: Your spine is made of lots of little bones called vertebrae, with squishy little disks in between them.
[6:27] SPEAKER_01: Okay, I feel them.
[6:28] SPEAKER_01: They feel pretty solid.
[6:30] SPEAKER_00: Down here on Earth, gravity pushes down on your body all day, squishing those discs like tiny heavy sponges.
[6:38] SPEAKER_00: But in space, the gravity squishing stops completely.
[6:42] SPEAKER_00: Oh, so without the squish, the spine just stretches out.
[6:46] SPEAKER_00: Exactly! The vertebrae expand and separate slightly.
[6:50] SPEAKER_00: NASA scientists, like principal investigator Dr.
[6:54] SPEAKER_00: Scott Dolchowski, have used special ultrasound machines to measure astronauts' spines while they are actually living in space.
[7:02] SPEAKER_00: And they found that astronauts grow up to 3% taller.
[7:06] SPEAKER_01: Wait, so a six-foot astronaut would grow two whole inches?
[7:10] SPEAKER_01: That's massive! But wait, do they shrink back down when they come home to Earth?
[7:15] SPEAKER_00: Yep.
[7:16] SPEAKER_00: Once they return to Earth's gravity, that invisible weight pushes down on them again, and they shrink back to their normal size after just a few days.
[7:25] SPEAKER_01: Phew! I was worried they would have to buy all new pants.
[7:28] SPEAKER_01: What about sleeping?
[7:29] SPEAKER_01: If there's no gravity, do you just sleep floating in the middle of the room?
[7:33] SPEAKER_00: You could, but that is actually super dangerous.
[7:37] SPEAKER_00: The air vents could blow you into a computer screen, or you could accidentally flip a switch.
[7:42] SPEAKER_00: So, astronauts sleep inside sleeping bags that are strapped tightly to the walls.
[7:48] SPEAKER_00: Strapped to the wall?
[7:50] SPEAKER_01: That sounds like you're sleeping like a bat.
[7:52] SPEAKER_00: It kind of is.
[7:54] SPEAKER_00: In the tiny crew quarters, they can sleep right side up, upside down, or sideways.
[8:00] SPEAKER_00: Because in space, without gravity pulling on your inner ear, your brain has no idea which way is up.
[8:06] SPEAKER_00: That is amazing!
[8:08] SPEAKER_01: But wait, if everything is weightless and you just float around everywhere effortlessly, does your body get really lazy?
[8:17] SPEAKER_00: That is a brilliant question, and the answer is yes, it absolutely does.
[8:22] SPEAKER_00: Without having to push against gravity every time you stand or walk, your muscles and bones start to get weak very fast.
[8:30] SPEAKER_00: How weak are we talking?
[8:32] SPEAKER_00: It's pretty extreme.
[8:34] SPEAKER_00: In just six months living on the International Space Station, an astronaut can lose up to 10% of their bone mass.
[8:42] SPEAKER_00: On Earth, that could take four whole years to rebuild.
[8:54] SPEAKER_00: A lot.
[8:55] SPEAKER_00: Astronauts on the ISS are required to work out for two whole hours every single day.
[9:02] SPEAKER_00: Two hours?
[9:03] SPEAKER_01: But how do you even lift heavy weights if everything in space is completely weightless?
[9:08] SPEAKER_00: They use a brilliant piece of technology called ARED.
[9:13] SPEAKER_00: That stands for Advanced Resistive Exercise Device.
[9:17] SPEAKER_00: Instead of heavy iron plates, it uses vacuum cylinders to create resistance.
[9:22] SPEAKER_00: So pushing against it feels exactly like lifting heavy weights on Earth.
[9:27] SPEAKER_01: That is so smart! What about running?
[9:30] SPEAKER_01: Do they have space treadmills?
[9:33] SPEAKER_00: They do! They have a specialised treadmill called the T2.
[9:37] SPEAKER_00: But to use it, astronauts have to wear a heavy harness connected to bungee cords that constantly pull them down onto the running track.
[9:46] SPEAKER_00: Otherwise, one single running step and they would launch headfirst into the ceiling.
[9:56] SPEAKER_00: It's funny, but the exercise is super important.
[10:00] SPEAKER_00: Astronaut Scott Kelly spent nearly a full year in space, and doing those daily workouts kept his muscles and bones strong enough to walk shortly after he landed back on Earth.
[10:11] SPEAKER_00: The human body is incredibly adaptable when scientists give it the right tools.
[10:16] SPEAKER_00: Alright, Finn, it's time for the quiz! Let's see what you remember from today's deep dive into space.
[10:23] SPEAKER_01: Oh boy, I hope I paid attention.
[10:25] SPEAKER_01: I am ready.
[10:26] SPEAKER_01: Bring on the questions.
[10:28] SPEAKER_00: First question.
[10:30] SPEAKER_00: How fast does the International Space Station travel in miles per hour?
[10:38] SPEAKER_00: Next one.
[10:39] SPEAKER_00: What happens to fluids in the body when an astronaut goes to space?
[10:47] SPEAKER_00: Question three.
[10:49] SPEAKER_00: How much taller can an astronaut grow while living in microgravity?
[10:57] SPEAKER_00: Here's number four.
[10:58] SPEAKER_00: Why do astronauts have to strap their sleeping bags to the walls?
[11:06] SPEAKER_00: Last question.
[11:08] SPEAKER_00: How many hours a day do astronauts have to exercise to keep their bodies strong?
[11:16] SPEAKER_00: Great job! Let's see how you did on those.
[11:19] SPEAKER_00: The first answer is the ISS travels at a mind-blowing 17,500 miles per hour.
[11:28] SPEAKER_00: For question two, the fluids shift up into their chest and head, causing puffy face bird leg syndrome.
[11:37] SPEAKER_00: Number three, the answer is they can grow up to two inches or five centimetres taller.
[11:44] SPEAKER_00: Question 4.
[11:45] SPEAKER_00: They strap their sleeping bags to the walls so they don't float around and accidentally bump into important computer equipment while they sleep.
[11:54] SPEAKER_00: And the final answer is they absolutely must exercise for two whole hours every single day.
[12:01] SPEAKER_01: Wow, the human body is so incredible! And scientists are so smart for figuring all of that out.
[12:07] SPEAKER_01: But honestly, I think I am really glad gravity keeps my feet planted safely on the ground.
[12:14] SPEAKER_00: Me too.
[12:16] SPEAKER_00: I don't think I'm quite ready for the puffy-face bird leg syndrome just yet.
[12:20] SPEAKER_00: I like tasting my food without needing a gallon of hot sauce.
[12:24] SPEAKER_01: And I definitely do not want to strap myself to the bedroom wall like a bat just to get a good night's sleep.
[12:31] SPEAKER_00: If you loved learning about the wild world of space science with us, and you think you'd like to try floating in zero gravity someday, leave us a five-star review.
[12:40] SPEAKER_00: Just scroll down and tap the five stars on your podcast app.
[12:44] SPEAKER_00: Yes, please do.
[12:46] SPEAKER_00: It helps other kids find our show.
[12:48] SPEAKER_00: Oh, and don't forget to check out our site kidopoly.com.
[12:52] SPEAKER_00: We've got tons of fun learning games, cool science activities, and more episodes there.
[12:58] SPEAKER_01: It's awesome! And if you want a shout out on the show, or just want to say hi and tell us your favourite space fact, email us at hello at kidopoly.com.
[13:08] SPEAKER_00: Keep looking up at the stars, everyone.
[13:11] SPEAKER_00: See you next time on Science is Not Boring.
[13:14] SPEAKER_00: Bye, everyone!

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