Geyser Tube Science Fair Project Are you ready for the most explosive science fair ever? email to friend
print this page

Here are a few ideas you might want to try...

The Fairness Factor

Before the invention of the Geyser Tube™, everyone had a different method for dropping Mentos® into the bottle of soda. You might have used the test tube method while someone else made a tube out of notebook paper. Unfortunately, the method for dropping the Mentos® was never consistent. The Geyser Tube™ removes the inconsistency (make the drop the same every time) and lets you focus on the true variables (what you’re trying to test).

When you’re conducting the test below, you might want to remove the top cap of the Geyser Tube™. This will make it easier to record how high the soda shoots up into the air because the column of soda is bigger and stays together better. Make sense?

The Scale

You want to be able to easily record how high your geyser goes. One method is to select a launching site that is up against the side of a tall building. You’ll also need an adult to help you with the next part. With permission from the owner of the building, use chalk (and an adult helper) to mark off one foot increments on the side of the building. Since you’re a scientist, it’s best to use metrics for all of your measurements.

You might want to enlist the help of another adult who owns a camcorder. By recording every launch, you’ll be able to replay the tape in slow motion in order to get the best measurement possible. You see... science and technology go hand in hand.

How Many Mentos®?

It’s a question that everyone who does this project asks. What is the best number of Mentos® to use to make the highest shooting geyser? This is a great topic for a science project, but you’ll need lots of soda and Mentos® and a few friends to help record all of the data.

Let’s start with one single Mentos®. All of the bottles of soda should be the same and they should also be the same temperature. Use the Geyser Tube™ to make sure every launch is the same. You’ll also need a way to measure how high the soda shoots up into the air. Use a scale attached to the side of a building as one way to measure the height. It’s also a good idea to record each launch on video in order to go back and watch the launch in slow motion. Now you know your data will be accurate.

Attach the Geyser Tube™ to the top of the 2-liter bottle of diet soda. Push the trigger pin through the holes and load one Mentos® into the tube. You might decide not to attach the top cap – this makes it easier to record how high the soda goes because it’s not spraying everywhere. The launch site is ready... the Mentos® is loaded... the video camera is recording... and you pull the pin! Record the height (at least your best guess for right now). Repeat this same procedure for 2 Mentos®, 3 Mentos®... you get the idea. Based on your data, how many Mentos® do you need to make the highest shooting soda geyser?

Diet vs. Regular – The Geyser Showdown

When the Soda Geyser became famous in 2005, everyone debated if diet soda was better then regular soda for launching geysers. Many people (including Steve Spangler) chose diet soda because the lack of sugar meant no sticky mess. But, does diet soda perform better than its regular counterpart?

For this test, you might decide to test three brands of soda using both diet and regular. For example, regular Coke would challenge Diet Coke and Diet 7-UP would challenge regular 7-UP. Return to your launching site with the scale in place on the side of the building, the camcorder loaded with tape, and a whole pile of soda and Mentos®.

Attach the Geyser Tube™ to the first bottle with the pin in place. Again, you might want to leave the top cap off in order to make it easier to determine how high the geyser goes. You’ll need to use the same number of Mentos® for every launch. You can use the results from your last experiment (How Many Mentos®?) or just select a number like seven (which works very well!). Load seven Mentos® into the Geyser Tube™, make sure everyone is ready and pull the string. Make a chart to record your data.

Clear the launching site and set-up the challenger. Repeat the experiment and record your data. You might have to review the video to determine the winner. Continue the same procedure with every regular vs. diet soda challenge. You’ve got some great data and some amazing pictures for your science project.

The Brand Test

You guessed it... it’s time to put your favorite soda to the test. Does one brand produce higher flying geysers? How does generic soda stack up again the big name brands? Using the procedure outlined in the previous experiments, it’s easy to determine the clear winner. Remember, it’s important conduct each test the same way using the Geyser Tube™ and the same number of Mentos® for each launch. You’ll also want to make sure all of the soda is at the same temperature because temperature plays an important role in the reaction.

Just think... your results could help determine the next Mentos® Geyser craze.

The Temperature Test

How does the temperature of the soda affect the height of the geyser? Does a warm soda shoot up higher than a cold soda? The key to keep every launch fair and to make sure the only variable is the temperature of the soda. You’ll also need a thermometer to record the temperature of the soda just before you launch it into space.

It’s best to stick with one brand of soda for the entire test. Let’s decide to use Diet Coke. You’ll want to purchase three bottles of Diet Coke and several rolls of Mentos®. You’re going to set-up three tests: Warm soda, room temperature soda and cold soda. Place one bottle of Diet Coke in the refrigerator and let it sit over night. Place the second bottle in a place where it can reach room temperature over night. There are two safe ways to warm the bottle of soda. The simplest method is to let the unopened bottle sit in the sun for several hours. You can also place the bottle of unopened soda in a bucket of warm water. Never use a stove or microwave to heat a bottle of soda.

It’s time to return to your launching site. Check to make sure the scale is in place and the video camera is loaded with tape. Let’s start with the bottle of cold Diet Coke. Open the bottle and dip the thermometer down into the soda. Record the temperature on your data table. Attach the Geyser Tube™ with the trigger pin in place. Load seven Mentos® into the tube and get ready to launch. Pull the pin and record the data. Repeat the same procedure for the soda at room temperature and the warm soda.

Observations

Warm soda tends to fizz much more than cold soda. Why? The answer lies in the solubility of gases in liquids. The warmer the liquid, the less gas can be dissolved in that liquid. The colder the liquid, the more gas can be dissolved in that liquid. This is because as the liquid is heated, the gas within that liquid is also heated, causing the gas molecules to move faster and faster. So, they will diffuse out of the liquid, leaving less gas dissolved in that liquid. In colder liquids the gas molecules are moving very slowly, causing them to diffuse out of solution much more slowly, and more gas tends to stay in solution.

Did you know… At the bottling plant, carbon dioxide is pumped into the cans or bottles when the fluid is very cold—around 35 degrees Fahrenheit. This low temperature allows the maximum amount of carbon dioxide to dissolve in the soda.

How does it work?

Here's the question of the day... Why do Mentos® mixed with soda produce this incredible eruption? You should know that there is considerable debate over how and why this works.

While we offer the most probable explanations below, we also understand and admit that other explanation could be possible... and we welcome your thoughts.

As you probably know, soda pop is basically sugar (or diet sweetener), flavoring, water and preservatives. The thing that makes soda bubbly is invisible carbon dioxide gas, which is pumped into bottles at the bottling factory using tons of pressure. Until you open the bottle and pour a glass of soda, the gas mostly stays suspended in the liquid and cannot expand to form more bubbles, which gases naturally do.

But there's more... If you shake the bottle and then open it, the gas is released from the protective hold of the water molecules and escapes with a whoosh, taking some of the soda along with it. What other ways can you cause the gas to escape? Just drop something into a glass of soda and notice how bubbles immediately form on the surface of the object.

For example, adding salt to soda causes it to foam up because thousands of little bubbles form on the surface of each grain of salt. Many scientists, including Lee Marek, claim that the Mentos phenomenon is a physical reaction, not a chemical one.

Water molecules strongly attract each other, linking together to form a tight mesh around each bubble of carbon dioxide gas in the soda. In order to form a new bubble, or even to expand a bubble that has already formed, water molecules must push away from each other. It takes extra energy to break this "surface tension." In other words, water "resists" the expansion of bubbles in the soda.

When you drop the Mentos® into the soda, the gelatin and gum arabic from the dissolving candy break the surface tension. This disrupts the water mesh, so that it takes less work to expand and form new bubbles. Each Mentos® candy has thousands of tiny pits all over the surface. These tiny pits are called nucleation sites - perfect places for carbon dioxide bubbles to form. As soon as the Mentos® hit the soda, bubbles form all over the surface of the candy.

Couple this with the fact that the Mentos® candies are heavy and sink to the bottom of the bottle and you've got a double-whammy. When all this gas is released, it literally pushes all of the liquid up and out of the bottle in an incredible soda blast. You can see a similar effect when cooking potatoes or pasta are lowered into a pot of boiling water. The water will sometimes boil over because organic materials that leach out of the cooking potatoes or pasta disrupt the tight mesh of water molecules at the surface of the water, making it easier for bubbles and foam to form.

When a scoop of ice cream is added to root beer, the float foams over for essentially the same reason. The surface tension of the root beer is lowered by gums and proteins from the melting ice cream, and the CO2 bubbles expand and release easily, creating a beautiful foam on top Next question... Why should you use diet Coke or diet Pepsi? The simple answer is that diet soda just works better than regular soda. Some people speculate that it has something to do with the artifical sweetner, but the verdict is still out.

More importantly, diet soda does not leave a sticky mess to have to clean up. Hey, that's important.

What's the record for the biggest Mentos® fountain? My official record is a 18 foot blast that shot up and almost took out a half million dollar, high-definition television camera. You'll find video on-line at www.SteveSpanglerScience.com of some of our favorite eruptions.

On a personal note... I've performed this demonstration well over a thousand times - on television, talk shows, science conventions, teacher associations, for CEO's at huge motivational speaking rallies, for Nobel Prize winners and anyone else who might watch. And the reaction is always the same... that's amazing! My thanks to Lee Marek who originally shared the Mentos® idea with me and to the hundreds of teachers and science enthusiasts who continue to share their funny pictures, videos and experiences.