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Do you have bored kids at home on summer break? Grab a bag of cotton balls and a glass of water and prepare to blow their minds! In this activity you will challenge your kids to guess how many cotton balls can fit into a glass of water without overflowing the water.
It is exciting, entertaining, and magical to watch cotton ball after cotton ball get adsorbed in the glass of water. This is an easy activity that will wow your kids! I suggest getting a large bag of cotton balls, because they are going to want to do this activity over and over again.
I got the idea for this activity from a great reel by my favorite fellow engineering mom blogger, Tracey at She Loves Science. You can see her original reel by clicking here.
Watch the Activity:
You can watch our version of the activity on both my YouTube channel and my Instagram account. Both videos are embedded below, so you can watch the activity before getting started. The videos on each channel are slightly different, but share the same overall content so feel free to watch just one on your favorite platform or enjoy both!
Watch my YouTube video below:
Watch my Instagram reel below:
Activity Overview:
This is a magical science activity that will blow your kids’ minds as they see cotton ball after cotton ball get adsorbed into the glass of water without the water overflowing! It’s easy and entertaining STEM activity for kids. This activity is recommended for kids ages 3+.
Materials:
- Cotton balls (make sure they’re 100% cotton, like the cotton balls linked here)
- Clear glass
- Water
Safety:
Remind kids to not put the cotton balls in their mouth (they may look like a treat if kids haven’t seen them before, but explain that these are not edible and do not go in mouths).
I recommend setting down a table cloth or placemat before beginning this activity. This will help protect your table from accidental water spills. Have extra towels on hand to clean up any water spills to prevent slips or falls.
Once you are finished with the experiment drain the water in the sink, and then dispose of the cotton balls in the trash (or you can compost them because they’re biodegradable) – just don’t dump them down the sink!
Procedure:
- Fill the glass of water all the way to the top (it should be as close to the top as possible).
- First, ask the child if the cotton ball will sink or float in the glass of water?
- Next, ask the child how many cotton balls they think will fit into the glass of water before it overflows?
- Drop one cotton ball into the glass of water. Did it sink or float?
- It’s a bit of a trick question: it will float at first until the water enters all the cotton fibers, then it will eventually sink to the bottom of the glass.
- Continue dropping the cotton balls into the glass of water one at a time until the glass is full or overflows (it should be full of cotton balls before it overflows).
- Optional: Repeat again, using these opportunities to expand on the experiment:
- Fill one glass with very cold water and another with very hot water. Drop cotton balls into both glasses. Does the temperature of the water make a difference in how quickly the cotton balls sink and how many balls will fit into the glass?
- Fill an empty glass of identical size to the water glass with cotton balls. Will they all fit into the glass of water? If they do, refill the glass with cotton balls and keep adding them to the water to see how many glasses full of cotton balls will fit into the water glass.
STEAM Concepts Learned:
Ask your child to feel the cotton ball in their hand. It is so light it almost feels weightless – that’s because it’s mostly air.
Cotton balls are are made of many cotton fibers. Cotton comes from a plant, so its natural fibers are made of cellulose. Each fiber is like a little tube or straw that is hollow on the inside. So there is air inside each fiber and air in between the many cotton fibers making up the cotton ball, meaning the cotton balls are made of mostly air!
When you drop the cotton ball into the water, the water fills the space that was previously filled with air (which is most of the volume of the cotton ball). Therefore, the cotton ball makes very little difference in the volume of the glass of water.
If you did the expansion of the activity you will see that the cotton balls sink faster in the hot water. That is because hot water molecules are moving faster, so they can get into the air pockets inside the cotton balls faster and more easily than cold water (and this is why hot water cleans cotton clothes better than cold water).
My kids were really entertained with this activity. We repeated it until we ran out of cotton balls (hence the tiny water glass that we used for the pictures in the procedure section – we used all the cotton balls filling the tall glasses in the videos 😉 ).
We challenge you to see how many cotton balls you can fit into your glass of water. Let us know in the comments how it goes for you!
