This is an awesome summer activity that will leave you and your kids asking, “Is it magic or is it science?” You can do this activity inside using a large bowl or vase filled with water. My kids thought this experiment was equally fun and magical!
My kids were amazed as they watched me demonstrate the activity, and then they each wanted to try it on their own. It was easy for my 10 and 8 year old to do the experiment, but my toddler struggled a little with the motor skills required to plunge the cup VERTICALLY into and out of the water. She did it correctly about half of her attempts, and the other half she would tilt the cup, allowing water to leak in and the paper towel would get wet.
She still had fun, so it was not a problem for us, and it was a great way to learn the constraints of the activity: the cup must be kept vertical for it to work correctly.
Watch the Activity:
This is one of those activities where the video demonstrates it a lot better than pictures. I highly recommended watching the videos to get a feel for how easy this is and also how well it works! You can watch our video on YouTube below:
I also posted a reel on Instagram for this activity, please visit my @engineering_emily Instagram page, and watch the reel below:
Activity Overview:
This is a perfect summer activity for kids. Kids will be amazed as the paper towel “magically” stays dry after being submerged into the water inside the cup. This activity is recommended for all ages as an observational activity, and kids ages 3+ can try the activity on their own.
Safety:
Make sure to have towels on-hand to clean up spills to prevent slips and falls. It’s best to use a plastic cup and bowl for this activity so there is no concern of breaking glass during the activity. If a glass vase or bowl is used, use caution while handling them, knowing glass is a fragile material that is dangerous if broken.
Materials:
- Large bowl or vase
- Water
- Paper towels
- Plastic cup
Procedure:
- Fill the bowl or vase 1/2 full with water.
- Fold the paper towel into quarters, then firmly press it into the top of the cup (it must fit tightly in the cup).
- Turn the cup upside down and vertically plunge it into the water.
- Pull the cup back out of the water (keeping it vertical), and then check the paper towel inside the cup. Is it wet or dry?
- Repeat as many times as desired. Here are a few variations to experiment with:
- What happens when you tilt the cup instead of keeping it vertical? Did you see any bubbles come out of the cup into the water?
- Does it make a difference if you move the cup slowly or quickly inside the water?
- What happens when you use two or more paper towels? Do they all stay dry?
- What happens if the paper towel doesn’t fit tightly inside the cup?
STEAM Concepts Learned
This experiment teaches kids that air takes up space with its volume, just like a liquid or a solid. Kids can see water has volume by looking at it in the bowl, but they can’t see the air all around them. When the cup is flipped upside down and lowered into the water, the air remains in the cup. The water doesn’t enter the cup because air is less dense than water, so the air remains contained in the cup, on top of the water (remember, substances with a higher density will sink and the lower density will rise).
The paper towel will stay dry as long as the cup is lowered into the water and pulled from the water vertically – this keeps the air trapped in the cup. If the cup is tilted at all going into or out of the water, this will allow the air to rush out (and will create bubbles) and water will enter the cup, wetting the paper towel.
Why did the paper towel stay at the top of the cup when it was flipped upside down, and not fall out due to gravity? The paper towel stays at the top of the cup when it is tightly pressed into it due to adhesion. Adhesion is a force that causes dissimilar molecules to be attracted and attach to each other, in this case the paper towel and the cup. The paper towel stays in the cup due to adhesion forces after it is tightly packed into the cup. However, if the paper towel is not tightly packed into the cup, adhesion won’t hold it in place, and it will fall due to gravity.
My kids and I really liked this experiment – it felt like a magic trick to us, and was so easy to do! I’m sure you already have everything you need at home, so what are you waiting for? Go try it and wow your kids with this magical science experiment!
