Sinking Soda Surprise
Plug the drain, fill the sink with water, and take the plunge.
Plug the drain, fill the sink with water, and take the plunge with Steve Spangler’s floating science challenge. We all know that certain things float in water while other things sink, but why? Do all heavy things sink? Why does a penny sink and an aircraft carrier float? Think you know the answers? Well, get ready for a few amazing surprises!
- An assortment of unopened soda cans (diet, regular, brand name, generic)
- A large, deep container of water like a 5 gallon bucket or an aquarium
Note: Use standard 12 oz cans. Mini-cans will not work.
- Ask your audience the question, “Will this can of regular soda float or sink in the bucket of water?” After gathering everyone’s answer, place the can of regular soda in the water and notice that it sinks to the bottom. If the can of regular soda floats, you might have an air bubble trapped under the bottom of the can.
- Pick up a can of diet soda and pose the same question. Be sure to point out the fact that the cans are exactly the same size and shape and contain the same amount of liquid (compare the number of milliliters… probably 355 mL). Place the can of diet soda in the water. It floats! Wobble the can from side to side to show your audience that there are no bubbles trapped under the bottom. It still floats. Why?
- Let your group experiment with different kinds of soda. Why do the diet sodas float and the regular soda cans sink, no matter the brand?
Try the experiment again using salt water. Are your results any different? What if you continue adding salt? How much salt do you have to add before your results change?
Consider changing the temperature of the water or the temperature of the cans. Do either of those changes affect the results?
How does it work?
This demonstration is an excellent way to learn about density. We are all familiar with the basic concepts of sinking and floating. Objects less dense than water float, and those more dense than water sink. Empty cans float, rocks sink. This is only possible because of differences in density.
If both diet and regular soda cans are placed on a double pan balance scale, it would be clear that the regular soda is heavier than the diet soda. This demonstrates the difference between mass and volume. Mass refers to how much stuff exists within an object. If something is heavier than another object, it contains more mass. Mass is measured in grams.
Volume, on the other hand, refers to how much space an object occupies. For fluids, volume is usually measured in liters (L) or milliliters (mL). There are 1000 mL in one liter. This is what we were referring to when we told you that the cans contained the same amount of liquid - 355 mL. Since both cans have the same volume, the heavier can must have a greater mass. We can now conclude that the heavier can is more dense than the lighter can.
Diet sodas usually contain aspartame, an artificial sweetener, while regular sodas use sugar. Take a look at the nutritional information on the side of the cans. Notice how much sugar is in a regular soda (look under carbohydrates). Most regular sodas have about 41 grams of sugar. How much is 41 grams? Try 18 packets of sugar like the ones you might find at a restaurant! Yikes! That's a lot! Diet soda is flavored with a relatively small amount of an artificial sweetener (like aspartame) which is 200 times sweeter than an equal amount of sugar. Therefore, only a tiny amount of aspartame is needed. Both sugar and aspartame are more dense than water, which can be easily demonstrated by adding small amounts of each to a container of water (they sink). So it is actually a matter of how much of each is used. The 41 grams or so of sugar added to a can of regular soda make it sink. The relatively tiny amount of aspartame used in diet sodas will have a negligible effect on the mass, enabling the can to float.
Why do cans of diet soda float? It is all due to the fact that there is a little bit of space, called "headspace," above the fluid in each can of soda. This space is filled with gas, which is much less dense than the soda itself. It is this space above the soda that lowers the density of diet drinks just enough to make them float. Sugared drinks also have this headspace, but the excessive amount of sugar added makes the can more dense than water.
There is an easy way to calculate the density of the two types of soda to further examine why one floats and the other sinks. Mathematically speaking, the equation for calculating density is Density = Mass divided by Volume. You can calculate the density of both the diet soda and regular soda by dividing the mass (weight) of the soda (in grams) by the volume of the soda (in milliliters). You will quickly see that the density of the regular soda is greater than the density of the diet soda... so, one sinks and one floats!
April 23rd, 2012
Click the thumbnail below to see the video.
Missing the real reason
Tim Forkner - September 18, 2012
The real reason the diet sodas float is because of head space in the can. There is a significant volume of the can that is filled with gas and not diet soda. An aluminum can COMPLETELY filled with diet soda would definitely sink since the overall density of the can (aluminum is > 1 g/ml and the soda pretty much = 1 g/ml) would be higher than the density of the water.
Karen - May 10, 2012
When my students perform this lab we use sugar cubes to visually see the amount of sugar that is added to the Diet Coke can on the triple beam balance. We only get 4 to 5 sugar cubes and not the 18 packets of sugar that was viewed? Will have to measure the amount of sugar in the packets to see if perhaps the ratio is 2:1; however this would still fall short of the sugar amount that you ended up with? Any ideas why?
Regular Dr. Pepper floated
Barb Allan - August 16, 2011
We did the experiment several times and both the Diet Dr. Pepper and regular Dr. Pepper Float???? Why is that?
Dr Pepper floats!
Jodi Tillery - February 14, 2011
We did this experiment for a school science project. We used 2 diets- Diet Pepsi and Diet DP, and 3 regulars- Sprite, DP, and Pepsi. The Dr. Pepper floated!! Any explanation for this?? It defies the info in the explanation.
Jeanette Emmerich - October 20, 2010
For some reason this experiment will not work this year. We have used it for years and never had a problem but this year both cans floated. Is anyone else having this problem?
Audrey Hendrix - August 1, 2010
The experiment worked very well, I am just wondering why I had issues with Sprite. The majority of regular Sprite cans floated, only a few sank. Any answers? Thank you.
Valeria - April 27, 2010
WOW! I can't believe it! Me and my friend did soda surprise and it really worked. It was AMAZING!
There was a problem
Nathanael - April 19, 2010
I did the same experiment as you showed with 18 cans of soda. But I had one regular Sprite that would not sink. It had no air bubbles and I kept pushing it down but it kept coming back up. I wonder why this happened.
it really works!!!!!
Taunya - April 3, 2010
This is so amazing, and it really works!!!! you can even add 12 ounce cans of uncarbonated sugar juice and lemonade, even diet red bull and regular red bull. Fun, Easy, Amazing!