Do pumpkins float?

Using pumpkins to teach your child about floating and sinking

Nothing says Autumn like the sight of bright orange pumpkins. This is the time of year you see them everywhere. Why not use this special time of year to help your little one explore concepts like weight, displacement, size, texture, changes, growth and decay.

Pumpkin Sink or Float

What sinks and what floats? This is a fun experiment to do outside on a warm fall day. For this experiment, you will need a scale, a large plastic tub, water and objects. Choose a variety of objects such as marbles, old keys, metal spoon, wooden spoon, plastic spoon, an empty metal pot, and, of course, a medium sized pumpkin. You can print out the Sink or Float Chart and either print it out or download it, take pictures of your objects and insert them in the table.

Fill the tub about halfway with water. You want to leave room for the tub to fill without sloshing over the side. Lay the objects out next to the tub. Take the first object you have listed in the chart or randomly choose an object and either draw or tape a picture of the object in the first column. Let your child hold the different items in his hands and guess which ones are heavier. Then weigh the object on the scale. For the smaller items, a kitchen scale works beautifully. If you are using a bathroom scale, and the smaller items don’t register, just make the write down less than a pound.

Let your child guess which ones will sink in the tub of water, and which ones will float.

Then test your hypothesis. Place each item in the tub. Record what sinks and what floats.

Ask your child to think about why the pumpkin floats, even though it is far heavier than the metal spoon. Compare the pumpkin to the other objects that floated and ask why your child believes that some of these items floated, while other, far lighter things, sank.

Why Do Pumpkins Float?

This is a great follow up to the first experiment. For this one, you will need a scale, A large tub of water, a metal pot with a lid, a roll of masking tape, a plastic cup or scoop, a pumpkin, and a knife.

First, weigh the metal pot and the pumpkin. Then tape the lid to the pot. Place the pot in the water. Show your child how the empty pot floats. Remove the tape and the lid from the pot and float the pot in the water. Gove your child the plastic cup or scoop and ask her to scoop water out of the tub and into the pot. As the water fills the pot, watch how the pot sinks to the bottom of the tub.

Place the pumpkin in the tub of water. Show how it floats. Remove the pumpkin from the water and cut it in half. Show the child how the center of the pumpkin is hollow and filled with air. Place one half of the pumpkin in the tub. Observe how it floats like a little round boat. Ask your child to scoop water from the tub and pour it into the cavity of the pumpkin.

Unfortunately, unless you are a true pumpkin aficionado, you probably won’t know the thickness of your pumpkin’s rind when you buy it. If you have a thin-skinned pumpkin, it will sink as it fills with water. If your pumpkin has a thick rind, it will float even if it is filled with water. Either way, you have some fun observations to make with your child.

If your pumpkin has a thin rind and sinks, you can talk about how the pumpkin behaved just like the pot. The air inside the cavity kept it afloat while the pumpkin was whole, but allowed it to sink when it was cut in half and filled with water. You can draw parallels to the metal pot.

If your pumpkin has a thick rind, it may sink partially, but may not go totally to the bottom of the tub. This may confuse your child. If this happens, just pull out the half of the pumpkin that is not in the water. Look carefully at the rind of the pumpkin. You can see that it has tiny holes, or pores throughout the rind. These little air pockets will keep the rind afloat, just like the larger air pocket in the pot or the center of the whole pumpkin.

After exploring the pumpkin rinds, look at the seeds and “pumpkin guts.” Scoop out a handful of the pumpkin innards and place them in the water. You and your child will quickly see that the “guts” will sink to the bottom of the tub, while the seeds float to the top. When you look carefully at the seeds, you will see that they have a thin, clear membrane around them. This membrane protects the seeds from absorbing too much water. It also creates pockets of air that keep the seeds afloat.

Show your child that when you scrub the seeds between your hands in the water, the pumpkin falls to the bottom, leaving clean pumpkin seeds. Give your child an edible reward to the experiment with roasted pumpkin seeds. While many cultures just eat the inside of the seeds, pumpkin seed rinds are delicious and an excellent source of fiber.

Mix a half cup of salt with a gallon of water and soak your seeds in the solution overnight. The next day, preheat your oven to 250 degrees. Drain the seeds and spread them out on a cookie sheet. Roast the seeds in the low heat for two hours, or until they “pop.” You will hear the seeds pop as they completely dry. This may take one to two hours, depending on how moist your seeds are before you soak them in the salt solution. Eat them warm, or store them in an airtight container.

Download The Sink Or Float Chart

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