In Wonderopolis, we have lots of fun in the water. From paddling canoes and kayaks to spending time in houseboats, floating on lakes and rivers is a great way to enjoy the outdoors. When it’s too cold to be outside, sometimes we play with our collection of toy boats in the tub.

Once, we tried to take our pet rock collection for a swim. We were disappointed to see them all sink quickly to the bottom of the tub. Why did our rocks sink when our toy battleship, which is much heavier, floated along just fine? And how can barges carry so much cargo without sinking?

The science behind floating was first studied by an ancient Greek scientist named Archimedes. He figured out that when an object is placed in water, it pushes enough water out of the way to make room for itself. This is called displacement.

Have you ever experienced displacement? Of course, you have! Remember the last time you got into the bathtub and the water level went up? That’s displacement. When you got into the tub, water got out of your way to make room for you, so the water level in the tub got higher.

When an object enters water, two forces act upon it. There’s a downward force (gravity) that’s determined by the object’s weight. There’s also an upward force (buoyancy) that’s determined by the weight of the water displaced by the object.

An object will float if the gravitational (downward) force is less than the buoyancy (upward) force. So, in other words, an object will float if it weighs less than the amount of water it displaces.

This explains why a rock will sink while a huge boat will float. The rock is heavy, but it displaces only a little water. It sinks because its weight is greater than the weight of the small amount of water it displaces.

A huge boat, on the other hand, will float because, even though it weighs a lot, it displaces a huge amount of water that weighs even more. Plus, boats are designed specifically so that they will displace enough water to assure that they’ll float easily.

109 Join the Discussion

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    • Hey there, Wonder Friend Alvaro! The Titanic was believed to be unsinkable, which is why it’s an incredibly tragic story. When the ship hit the iceberg, it damaged the vessel and its ability to safely float. We Wonder what book you’re reading? It sounds great!

      Some Wonder Friends here at Wonderopolis have been on boats before… cruise ships, sailboats and pontoon boats! We Wonder if you have traveled by boat? :)

        • How WONDERful, Jagger! We are excited for you to embark on a Wonder Adventure all about boats! We suggest you visit your library to do research online and in books to find ideas! You could even ask your librarian to help you begin! :) Happy WONDERing, friend!

  1. Wow I didn’t know that about boats thanks for teaching me somthing new every day. By the way I’m in Mrs. Hess’ class I will go to school in 30 minutes.

    • We’re glad you learned something new with us today, Joaquin! We hope you have a SUPER day at school– say hello to our Wonder Friends in Mrs. Hess’ class! :)

  2. Thoughts: We learned that when heavy objects are shaped the right way, they can float. We’re curious how many different types of shapes can be used so that items float. Where do boats come from? Plastic boats will float because they are less dense than the water. Who invented the first boat?

    Predictions: Who wrote the original story of The Three Little Pigs? Why do wolves eat pigs? Do wolves have emotions? When was the original story the Three Little Pigs written? Who invented boxing? Can pigs eat wolves? How do buildings collapse? How many different variations of The Three Little Pigs are there? How are hurricanes formed? Why do we sneeze?

    Have a great day. :)

    • Hey there, Wonder Friends in Mrs. Hess’ Class! We’re so excited that some of you have been visiting us lately– even on the weekends! :) WAY TO GO!

      You have a WONDERful question about the first boat invented; no one is absolutely certain! Many believe Egyptians were the first to build ships, but even before then, people would create boats out of logs and bundles of reed. We bet you can find out some more information about the very first boats with some help from your librarian!

      Thanks for sharing your SUPER guesses for tomorrow’s Wonder! We’re so proud of you! :)

    • Thanks for sharing your comment, Kenneth V! We’re so glad you enjoyed today’s floating Wonder– we sure learned a lot! The pufferfish sounds really cool, thanks for letting us know what your guess is! :)

  3. Good Morning, Wonderopolis! Thank you so much for teaching us about how boats float! We now know why the water rises when we get in the tub! We also now know about buoyancy and how boats and objects float! Have a wonderful day!

    • Good morning, Wonder Friends in Miss Hobson’s Kindergarteners! We are so glad you learned a new thing or two with us today. You really make WONDERing fun! We hope your day is float-tastic! :)

  4. Good Morning, Wonderopolis!
    Thank you for today’s awesome wonder! We are still wondering some things… When a boat goes into the water, why doesn’t the water rise? Or does it and it’s just hard for us to tell? Do bigger boats float better than smaller boats because they take up more space in the water? We predict that tomorrow’s Wonder will be about The Three Little Pigs. Maybe the Wonder will be, “Why does the wolf want those particular pigs?” We wonder why he didn’t just find some other pigs!
    Have a great day! (It’s our 100th day of school! Yippee!)

    • Good morning to our Wonder Friends in Mrs. Plunkert’s Class! You’ve been doing a great job of WONDERing on this marvelous Monday morning! We learned about a term called displacement, which is hard to see with our own eyes. That’s because water is fluid, or always moving. But displacement describes what happens when we put anything in water. Think of when you draw a bath. If you marked the waterline of the bathtub, and then got into the bathtub, you’d see the water rise. That’s displacement! HOORAY!

      We LOVE WONDERing with you, and we hope your 100 day is WONDERful! :) We’ve got a Wonder for your special day: Wonder #100 of course! :-)

    • Great point, Patrick! The very first boats were shells– even hollowed out logs tied together with reeds! We’re so glad you’re here today! :)

    • We’re glad you’re here today, Wonder Friend Pink! We like using context clues to help us understand new or big words! We are proud of you for WONDERing with us today- great work! :)

  5. So if a ship is hit by an iceberg a hole is created in the side of the ship’s hull so then water takes up the space inside the ship where there is no water and it is dry so then the ship fills up with water until it sinks.

    • You’re quite right, Wonder Friend Hunter. That’s the issue with ships– they can float, unless they hit something. We’re so glad you have been WONDERing with us today- nice work! :)

    • Great question, Ryan M! Today’s Wonder asks that same question– how interesting! It’s all about displacement, or how much water is moved when something is placed on top of it! A rock is tiny and heavy, and not much water is displaced when you drop it in the water– it sinks! However, a boat, when built correctly, displaces a lot of water because of its size. We know it can be tricky at first, but give the Wonder another try– we know you’ll get the hang of it! :)

  6. It is cool that wood floats but how does a boat float it is much bigger and made at metal, From Beaux. I learned that if the density is lower than the weight of the object, it sinks. From Kenny. Even though the boat is bigger it still has more density which makes it heavier but why does it not sink also medal is heaver. From Beaux. So actually the more matter an object has, the higher chance it has of sinking. From Kenny.

    • Hey there, Wonder Friends Beaux and Kenny! You’ve both been doing a marvelous job of WONDERing with us today! Thanks for sharing all the cool new things you’ve learned about boats, buoyancy and matter! Keep up the SUPER work! :)

    • Hey there, Wonder Friend Mystery! A lot of people thought the Titanic was unsinkable, and unfortunately there were other things that affected its ability to stay above water. Thanks for sharing your comment with us today! :)

  7. Mrs. Goneau’s Second Grade Class

    We were wondering…

    Can a boat still float when it gets damaged above the water?
    How much do large boats weigh?
    Is a canoe shaped different on the bottom than a cruise ship?
    How many people can a large cruise ship hold?
    How do aircraft carriers float with all the heavy aircrafts?
    What kind of fuel does a large boat need to run?
    How fast can a ferry boat travel in one hour?

    • WOW, we are so impressed with all the awesome Wonders from our Friends in Mrs. Goneau’s Class! Nice work! :)

      Damage to a boat can cause it to sink, that’s how many shipwrecks occur. It depends on the type of boat, but damage to a ship can impact its ability to float. You can Wonder more about shipwrecks with Wonder #694:

      We did some WONDERing about cruise ships, and the largest one out there can hold a whopping 5,400 passengers! The absolute maximum number of people is 6,360! PHEW!

      We know you have LOTS of Wonder questions to research, but we think you’ll enjoy this boat-tastic Wonder about Venetian transportation: Wonder #744– What’s a Gondola? :)

      Thank you for visiting us today! :)

  8. I think I can relate to this passage because in my science class I am learning about pull and push factors and gravity and mass and weight and volume so NOW I know why BOATS float…..

    • WOOHOO, that’s like music to our ears, Andre’yanna! We’re so glad that our Wonder connects to your lessons in class!! We love to learn new things, especially when we’ve started studying them in school. HOORAY for push, pull, gravity and mass! :)

    • That’s great to hear, Marc, we’re so glad you enjoyed today’s floating Wonder! We look forward to WONDERing again with you soon! :)

    • You’re right, Morgan3222! It’s fun to learn something new each and every day! Thanks for sharing your comment with us today- we’ll see you soon! :)

    • We’re lucky to have a great Wonder Friend like you to share these floating facts, Andre’yanna! Thanks for sharing your comment! :)

  9. I remember when I used to play with toy boats. Those were some good times. Ha-ha. Yeah, well, I liked today’s Wonderopolis.

    • Great memories, Gina M! Thanks for connecting your memories and today’s Wonder! We’re glad you’re here, Wonder Friend! See you soon! :)

  10. This is so cool that is why boats don’t sink. I always thought the rock would float and the boat will sink. =)
    Wonderopolis answer me back. =)

    • Hey there, Jesse T! Thanks for telling us about what you learned from today’s Wonder! The science of floating is super cool! We’re glad you’re here today! :)

  11. We never knew you could shape metal/steel to make a boat float! Pretty cool!

    We think tomorrow’s wonder will be about fairy tales, tornados, or wind (we live in Oklahoma where the wind comes sweeping down the plain!)

    • Hi there, Wonder Friends in Mrs. Brandon’s 3rd Grade! Thanks for WONDERing with us today! We’re so glad to hear you learned something new with us today– perhaps some of you will construct a boat of your very own in the future!

      Thanks for sharing your comment today- and telling us where you’re WONDERing from! We hear the wavin’ wheat, it sure smells sweet in Oklahoma! ;)

      Thanks for sharing your awesome guesses with us! :)

    • Hey there, Wonder Friend Annon! We’re glad you asked! This vocabulary word, buoyancy, describes something with the ability to float! Today’s Wonder is all about buoyant boats! :)

    • Great question, Hannah! There are lots of different types of boats– some have paddles, some have motors, and some have huge engines! Boats can float even if they don’t have a motor! How cool! :)

  12. Dear wonderopolis
    I think today’s video was really cool I had never learned about buoyancy before and I think it is really cool!!!

    • Science is awesome, just like you pandalover! Thanks for sharing your comment with us and telling us about what you learned today! Nice work! :)

  13. HIIIIIIIIIIIIIII!!!!!!!!!!!!!!!!!!! Hellooo WONDEROPOLIS!!!!!!!!!!!!!!! I REALLY LIKED THE VIDEO FOR THIS WONDER (very educational by the way)!!!!!!!!!!! THIS IS MY FIRST TIME COMMENTING!!!!!!! I AM SO HAPPY RIGHT NOW!!!!!!!!!!! I love you wonderopolis!!!!! :)

    • WOW, thanks for sharing your super enthusiastic Wonder comment, happygirl! We’re so glad you’re WONDERing with us today– WELCOME! :)

    • Boats that are well-made can float, Justin, unless something unfortunate happens (like it did for the Titanic). We’re glad you’re WONDERing with us today- keep it up! :)

  14. I think that how do boats float is a very good topic to explain about and to talk or learn about.

    Prediction: A Wolf from the big bad wolf or did it really happen.

    • Hey there, tigerlover! Thanks for sharing your thoughts about today’s Wonder- we’re glad you did! We also really enjoyed your guesses for tomorrow’s Wonder of the Day®! Great imagination! :)

  15. How do things float? Buoyancy helps lift the plastic from water. And the thing you want to float has to be lighter than the water. Anything can float if you shape it right even metal it all has to deal with buoyancy that is why plastic can float.

    • Great work, Daniel T! Thank you for sharing what you learned about floating and buoyancy today! HOORAY for you! Shape has a lot to do with an object’s ability to float! :)

  16. I learned that when somthing is light it can float but if something is hard it can’t float it will sink. I am wodering what will be the other interesting thing that will be come up on wonderopolis! Thank you for the sharing! :]

    • We’re so glad you’re here, Wonder Friend Crystal! Thanks for sharing what you learned about floating objects– don’t forget about the push and pull of forces and gravity! Science is cool, especially when you can try it out yourself! Thanks for WONDERing with us, and we hope to see you soon! :)

    • Hey there, Duck Dynasty Girl! We’re glad you asked about floating and moving at the same time! We know that boats can float, but some use an engine to move from place to place. Boats need a force to propel them, or move them forward. However, for smaller boats all you need is a paddle and some upper body strength! Thanks for sharing your comment! :)

    • Thank you for sharing your Wonder guess, Duck Dynasty girl! We think it’s great that you’re using your imagination with us today! HOORAY! :)

  17. How do boats float if they don’t have anything to paddle with? And the person that drives it do they have to be strong to turn it?

    • Great questions, Crystal! We learned that science is a big part of understanding how boats float. The boat has be shaped a certain way in order to float– so many boats don’t even need paddles! We Wonder if you can make a list of all the different boats you have seen or heard of… or perhaps use the Internet to find out more information! You can see how some boats have paddles, some have engines, and some need captains! :)

    • Thanks for sharing your comment, Victor! We LOVED learning about how boats float with you! We can’t wait to Wonder again soon! :)

    • We’re so glad are here to learn something new with us, Laila! The Wonder video and article are full of great information! :)

    • Hey there, Chase! We bet Minnesota was very cold– we hope you were bundled up! Thanks for sharing your cool comment with us- what a great connection to our boat Wonder! We hope you have a WONDERful Wednesday! :)

    • We’re so glad you enjoyed our adventure on the sea, Aniyah! Science is super cool, especially when we can Wonder with you! :)

    • Thanks for sharing your thoughts, Wonder Friend! We learned about push and pull with our boat Wonder. The water pushes up while the force of gravity pulls down, allowing the boat to float! :)

    • Hey there, Wonder Friend Courtney! While some lighter boats have no trouble floating, we can’t forget about those big boats that sail through the ocean! It has to do with displacement… check out the excerpt below for more information!

      “This explains why a rock will sink while a huge boat will float. The rock is heavy, but it displaces only a little water. It sinks because its weight is greater than the weight of the small amount of water it displaces.
      A huge boat, on the other hand, will float because, even though it weighs a lot, it displaces a huge amount of water that weighs even more. Plus, boats are designed specifically so that they will displace enough water to assure that they’ll float easily.”

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Have you ever wondered…

  • How do boats float?
  • What is displacement?
  • Can you build a toy boat that will float?

Wonder Gallery

BoatVimeo Video

Try It Out

Ahoy matey! Did today’s Wonder of the Day really float your boat? Set sail with a few friends or family members to explore one or more of the following activities.

  • What kinds of things float? What things tend to sink? Make a list of things that float and sink and compare and contrast the items on your list. What do the things that sink have in common? What about the things that float? Does that match up with what you learned in today’s Wonder of the Day? Don’t limit yourself to things in the water either! Can you think of things that float in the air? What about clouds? Have fun brainstorming!
  • Ready for some bathtub fun? Pick out one of the crafts below and make your own homemade boat! Be sure to check the list of supplies, just in case you need to go to the store first to get something you’ll need.

When you’re finished, fill up the bathtub and test out your craft! Is it seaworthy? Does it float? Test it out against some non-floating objects, such as rocks, to see firsthand the principles discussed in today’s Wonder of the Day!

  • Are you familiar with the story of the Titanic? You probably are. You may have even seen the movie that was made about the famous oceanic disaster. Did you know that the Titanic was called the “unsinkable” ship? Can you imagine that? They sure were wrong, weren’t they? Just about anything can be made to sink. Do some research to learn about the most buoyant things on Earth. Some things just seem to float really well. Think of a ping pong ball, for example. Can you imagine it sinking? Probably not unless there was a hole in it. If you have a ping pong ball, test it out. Will it sink on its own? What about if you put a small hole in it? What do you have to do to make it sink? Can you find any other items that are almost unsinkable? Share your findings with your teachers and classmates at school!

Still Wondering

In Science NetLinks’ Buoyant Boats lesson, children will design and construct a boat that takes into account buoyancy, materials and design.

Wonder What’s Next?

You can huff and puff, but you won’t blow down tomorrow’s Wonder of the Day!

Upload a Photo or Paste the URL of a YouTube or SchoolTube Video.