2013
Sep 26

Carrot Canoes and Archimedes’ Principle

by Hannah Holt »

9 comments


I’m working on a new picture book about buoyancy, so I’ve had boats on the brain lately. Like, could you turn a carrot into a boat?

carrot boat 1

Carrots don’t float. Well, I supposed if you found a dried out carrot it might float, but for the most part carrots sink.

carrot boat 2

{See, I cut off the end of a carrot and put it in water… Thunk! It sunk.}

But what if we took a carrot peeler and hollowed out the inside of a carrot?

carrot boat 3

Ta da! It floats…

carrot boat 4

Now why does the first carrot sink while the second carrot floats? They are both carrots, right?

Let’s talk about buoyancy. Buoyancy is the lift water gives you. You might have noticed you feel lighter jumping in water than on land. That’s because the water pushes you up.

Weee2

How much does water push you up?

water weight

It pushes you up… the weight of the water you just replaced? Or as Archimedes Principle states:

Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.

Wow, that was a lot of words! Let’s go back to our carrot. Before we hollowed out our carrot, water still pushed up on the carrot. But the carrot was heavier than the amount of water it moved. In other words, it was too dense. So it sank.

carrot before and after2

In the second case, the carrot was lighter. The water could hold it up and it floated. You can make a carrot into a boat!

A few activities by grade-level:

Kindergarten-1st Grade: Take a potato, an apple, a carrot, and a pea. What ones float? What ones sink? Make a hypothesis: What else do you think will float? Now test it.

2nd -3rd Grade: I started with 2 cups of water (about 500 mL). The carrot and the water together have a volume of 2 ¼cups (about 525 mL). How big (in volume) is the carrot? Answer: ¼ cups big (or about 25 mL in volume)

4th – 5th Grade: One milliliter of water (volume) has a mass of one gram. The carrot took up 25 milliliters of water. How many grams of water did the carrot replace? Answer: 25 grams {You might have to walk them through this.}

6th Grade: Archimedes’ Principle says that the buoyant force on our carrot can be found like this:

The Volume of the Water (displaced by the carrot) x The Density of the Water x Gravity

If the Volume of the Water = 25 (cm³)

and the Density of the Water = 1 (g/cm³)

and Gravity = 10 (m/s²… I rounded for calculating ease.)

What is the buoyant force on the carrot?

{Answer: 25 x 1 x 10 = 250 g• m/s²} Advanced students might be interested in the units, but the main goal here is to try and plug the values into the equation.


  1. Susanna Leonard Hill

    Wow! Hannah! You’re so science-y! And you explained that so well that even I understood it! Now, if you’ll excuse me, I’m going to make a canoe out of a carrot :)

    • Hannah Holt

      Happy canoeing! :)

  2. Aunt Ginger

    Hannah,

    You did a very good job explaining this scientific principle. I look forward to further scientific episodes!

    Aunt Ginger

    • Hannah Holt

      Thanks, Aunt Ginger… more in the works. :)

  3. Carrie F

    Cool explanation! I like your experiment – very relatable for young kids.

    • Hannah Holt

      Thanks, Carrie. You know all about my boat trouble. 😉

  4. Tina Cho

    Great explanation! I’ll have to keep this for reference!

  5. Romelle

    You never cease to amaze me, Hannah!

  6. Erik - This Kid Reviews Books

    I learned a lot – like why big trees sink, but the Native Americans’ canoes (made out of the big trees) float (just imagine the carrot is the tree)! 😀