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One question that has come up (pun intended) from previous posts in this blog is why do pumpkins and apples float? To answer this question, we first need to look at why things float in general.

Do you still have your bin of water? Let’s try floating a few more things.

People have been wondering why things float since olden times. According to legends the ancient Greek, Archimedes, conducted experiments to test why things float or sink. Supposedly he figured it all out while sitting in the bathtub. Our modern interpretation is called Archimedes’ Principle.  It states that a body floating in a fluid is supported (or buoyed up) by a force equal to the weight of the fluid it displaces.

Let’s choose water as our fluid. Do you know how much a cubic centimeter of water weighs? How about a gallon?

A cubic centimeter of water weighs 1 gram by definition. A gallon of water (at a given temperature of 4 degrees C) weighs 8.34 pounds. So, in order to float, an item that weighs 1 gram must displace more than a cubic centimeter of water. An item that weighs 8.34 pounds must displace more than a gallon of water to float.

To test this, obtain a piece of modeling clay. Shape it into roughly a cubic centimeter. See if it will float. It will probably look something like this:

sunk

(Clay at the bottom).

Now, flatten out the same piece of clay and make a boat shape. A flat bottom with a lip around the edge works well. Place it onto the surface of the water. It should displace a lot more water this time and float. Although the weight of the clay didn’t change, the amount of water displaced did change.

float

Have you tried floating a can of diet soda versus a can of regular soda? Both are the same size and shape, will they both act the same when placed in water?

Here’s a silent video demonstration.

Why don’t the two identical objects act the same way? According to the box at the bottom of this How Stuff Works page, diet soda has less sweeteners added, so it actually weighs slightly less for the same volume than regular soda. Because they are both mostly water, that slight change is enough to allow diet soda to float. Cool!

Apples and pumpkins are not solid. The pumpkin has a large hollow inside. Both weigh less than the amount of water they displace, and thus they float.

Try floating pumpkin seeds. What about apple seeds? Do they float?

We found that pumpkin seeds floated, but apple seeds did not. The pumpkin seeds are flat and displace an amount of water roughly equal to their size. On the other hand, apple seeds are compact and round. They displace little water. They don’t have to be very heavy to sink.

A few years ago, our family participated in a contest to build a working boat out of cardboard. We started by investigating various boat designs and materials by floating models in a tub. We learned a lot about sinking and floating. You might want to make some paper boats and try them yourself.

Enjoy!

Instructions to make a Classic paper boat

Another cool design for a paper boat that works well.

Edit: check out this video of a huge pumpkin made into a boat.

Don’t you love going to the grocery store this time of year, with all the pretty pumpkins and fresh apples? Wouldn’t it be fun to use some pumpkins and apples for science activities?

Gather:

  • Pumpkins and apples. Get some different sizes, kinds and colors, if possible.
  • Bathroom/kitchen scale (depending on activities you choose)
  • Container, such as a large plastic bin, to hold water
  • Age-appropriate cutting implement
  • Trays for holding fruit parts
  • Paper
  • Pencils/crayons.

Activity 1. Exploration/Botany Vocabulary
Have your children look at the pumpkins and apples. How are they different, how are they the same?

Both pumpkins and apples are fruit. They both have seeds inside. Both have stems, can you find the stem? What is the stem for? Apples have a skin, does a pumpkin? (Yes, it does). You can ask older children what they think the fleshy meat (the part we eat) is for. Do both pumpkins and apples have a flower or blossom end?

Activity 2. Sorting
Have the children sort the pumpkins from the apples. They can also sort the sizes, from smallest to biggest, or by color. (Sorting is such an important scientific skill, one that tends to get forgotten.)

Activity 3. Weight Estimation
Have the children estimate how much they think each pumpkin/apple weighs. Ask them how they would weigh a big pumpkin.

Help them weigh the pumpkins and apples.

Activity 4. Pumpkin/Apple Floating
Will a pumpkin float? Will an apple float? Does how big it is determine whether it floats or not?

Fill up a large container with enough water to float the biggest pumpkin without slopping over. See if the different fruit will float or not. Have the children bob for apples, if appropriate. Have the children draw what happened.

Activity 5. Seed Estimation
Have the children estimate how many seeds they think are inside each pumpkin or apple before you cut the fruit open. Write down the estimations and compare with the results when you open them in the next activity.

Activity 6. Pumpkin/Apple Exploration
Begin to cut into the pumpkins by cutting around the stem, like you were going to make a jack-o’-lantern. Allow the children who want to explore to get their hands inside. Let them feel the seeds.

Cut the apples and allow the children to search for seeds. Have them count the apple seeds. See if slices will float differently than whole fruit.

Activity 7. Let It Rot!
Rotting or decay is a mysterious and fascinating process for children. In our modern ultra-clean world of antibiotics and hand sanitizers, we forget what an important process it is. If at all possible, find a quiet corner in the yard and let the pumpkin or apple rot. Check the progress daily. Admire the molds that develop. Discuss the odors. If rotting isn’t progressing, add a bit of water.

Activity 8. Grow or Eat the Pumpkins Seeds
You might want to save some of the pumpkin seeds to grow. If so, wash them and let them dry. Don’t heat them/cook them if you want to plant the seeds. Check one of the websites below for more information on growing pumpkin seeds.

Activity 9. Eating

You can oven-dry some of the pumpkin seeds for eating.

Celebrate Fall by making some of your favorite recipes. Here’s one of ours:

Pumpkin Pie in a Glass Smoothie

Add to blender:

1 to 1 1/2 cups canned or pureed cooked pumpkin
2 cups milk, soymilk or ricemilk
1/3 cup sweetener such as maple syrup
1 cup tofu
1 tsp cinnamon
dash nutmeg
1/4 tsp cloves

Blend until well mixed. Makes 4 8oz. Servings.

Early Learning Ideas website has many more excellent lessons for preschoolers.

Related Books:

Pumpkin Circle: The Story of a Garden by George Levenson, Shmuel Thaler (Photographer)

I love this book because it isn’t afraid to show rot.

Check this list of Fall–inspired books from the MissRumphiusEffect Blog.

Patty's Pumpkin Patch by Teri Sloat

Follow the progress of a pumpkin patch through the seasons while finding items from the alphabet. For example, in the field where the pumpkins are being planted, “a” is for ant and “b” is for beetle.