Why does Diet Coke Float and Regular Coke Sink?

When my kids were younger we were always looking for ways to “entertain” them. One way we did this was through an exciting science experiment or two. The messier they could get, or the more we could amaze them – the better the day went! Our students aren’t much different!

Why does Diet Coke float and regular Coke sink? Students explore density and buoyancy through this engaging science experiment activity on physical matter!

Remember the other day when I posted about density and wanting something new? (If not, it was a great post [with a freebie!] about creating your own lava lamps. You can check that post out here.)  Well, my husband reminded me that we use to entertain our masses with the magic of the floating diet coke!

My son is a huge science buff. So naturally when I mentioned this density and buoyancy experiment (or demonstration) his interest was piqued. Why do diet soft drinks float and regular soft drinks sink? If both cans are the same size and have the same amount of liquid… Shouldn’t they also be equal with their buoyancy? Ah, but of course there is one small factor… Density!

When I complete this science experiment in my classroom, I bring in a plastic clear Rubbermaid tub (but you could use an aquarium too) and set it up ahead of time before the students enter the classroom. I place my diet drink and my regular drink inside the tank. Then I just leave it. I wait for the questions to begin… Inquiry at its finest!

Once I convince students that I didn’t do anything to the cans or that it’s not magic, we begin exploring it together. What is different then? We work through my density science tabbed booklet and explore the investigation together. Then we discuss – is there anything else that may affect it? What about using salt water? Does the temperature of the water matter? What if we dump out just a little tiny bit of the diet?

Ultimately, we end up discovering that really, it’s the density difference in the two cans that creates a difference in the buoyancy. In regular soft drinks, there is more sugar packed into the same space as a diet. The diet uses artificial sugar. It takes less artificial sugars to create the same taste like regular sugar, so less is needed. That means in the diet, there is less matter packed into the same space – and it floats!

Though it’s not magic, it definitely doesn’t take the magic out of this fun science experiment!

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