How to Make a Diet Coke and Mentos Rocket
To make a Diet Coke and Mentos rocket, start by sandwiching 5 stacked Mentos between 2 4-inch strips of masking tape. Then, wrap a 3-inch strip of tape sticky-side out around your finger to make a piece of double-sided tape. Stick one side to the top of your Mentos stack and the other to the inside of a diet soda cap. You can use any 2-liter diet soda, as long as it contains aspartame. Once you've attached your Mentos to the soda cap, wrap another strip of tape around the bottom to make sure the Mentos don't fall apart. After you've finished taping the Mentos, head to a wide-open space like a field or empty parking lot, since the bottle will probably bounce around a lot and make a mess. Twist the cap onto the bottle, give it a big shake, and throw the bottle into the air.
Buy 1 2-liter bottle of Diet Coke. For the purposes of this example, we're using Diet Coke, but you can actually use any type of diet soda (as long as it contains aspartame). Warm soda causes better explosions, so avoid using cold/refrigerated soda. For best results, purchase room-temperature soda and then let it sit outside in the sun or in a pot full of hot (not boiling) water for a few hours before using it. Buy 1 package of Mentos. Experiments have shown that while the original Mint Mentos will give you a longer explosion, Mentos Fruit will give you slightly shorter but more intense explosion. Other experiments have shown that Mint Mentos are the better choice because the gum arabic found in the mint coating reduces surface tension and quickens the carbon dioxide's escape from the bottle, making for a more intense explosion. As the rocket is more of a fast-acting affair, you might want to go for Mint Mentos. If you have the time and money to do so, why not try one bottle with Mint Mentos and one with Fruit Mentos, and then compare the results? Obtain one roll of masking tape. You probably have this one lying around your house already, but if you don't, you should be able to buy a roll just about anywhere (hardware stores are a safe bet). Buy protective goggles. Wearing goggles will not only protect your eyes from the soda-Mentos concoction, but also from any other debris (for example, the lid) that might fly out from the bottle once it hits the ground and explodes. Find a wide-open space to build the rocket in. Your rocket is likely to bounce around like crazy; make sure it has enough room to do that. If you're in a parking lot, make sure there are no cars nearby for at least a 50-foot radius, if not more. If there's a field or empty lot nearby, go there to make your rocket. You don't want to risk doing damage to anyone's car or home, as it could cost you or your parents a lot of money to repair. Wear appropriate attire. It's possible you'll get covered in the sticky Diet Coke-Mentos solution. Wear clothes and shoes that you don't mind getting wet and sticky — preferably ones that are easy to wash. Gather your materials. Bring your 2-liter bottle of Diet Coke, your pack of Mentos, your masking tape, and your safety goggles to wherever you've decided to build your rocket. Cut 2 4-inch (10.2-centimeter) strips of masking tape. Place the strips of tape on a flat surface, with their sticky sides facing up. Do not allow them to stick together. Remove 5 to 7 Mentos from the roll. The more Mentos you use, the better the explosion; however, you don't want to the Mentos to dip too far into the Diet Coke otherwise the explosion may begin before you can screw the lid on the bottle. Lay the Mentos on to one of the 4-inch (10.2-centimeter) strips of tape. They should look just as they did when they were still in their original packaging: stacked on top of one another like a roll of coins. Place the other 4-inch (10.2-centimeter) strip of tape on top of the Mentos. Be sure to leave the sides of the Mentos exposed. Cut a 3-inch (7.62-centimeter) strip of masking tape and roll it around your finger, sticky side out. You'll use this piece to attach the Mentos to the bottle cap, so ensure that it's small enough to fit inside the cap. Attach the rolled tape to the top of the Mentos. Take the 3-inch strip of sticky rolled tape that you've just created and attach it to the top of the taped roll of Mentos. This will create a ”loaded” Mentos cartridge that you can place inside the Diet Coke bottle. Fasten the Mentos cartridge into the bottom of the Diet Coke cap. Put the cap on a flat surface, with its inside facing upwards. Place the Mentos cartridge, sticky-tape side up, into the soda cap and press down to fasten it there. Be careful not to press too hard, as you don't want any Mentos falling out of the cartridge! Double tape the cartridge to the cap. This step is optional. If you're worried about the Mentos prematurely falling into the Diet Coke, you can secure the cartridge by running one more piece of masking tape around the entire roll, including the cap. Twist the “loaded” cap on to the Diet Coke bottle. The cap should be securely on the bottle, but not closed too tightly. If it's closed too tightly, the cap might not come off when you throw the bottle, and the rocket won't work. As you twist the cap on, you'll also want to make sure that the Mentos do not touch the Diet Coke yet. If it seems like the Mentos will touch the Diet Coke, you can either dump a small amount of Diet Coke out before screwing the cap on; redo your Mentos cartridge to contain fewer Mentos; or you can try your luck and screw the cap on as quickly as possible. Shake the bottle. Shake it so that the Mentos fall into the Diet Coke, and then keep shaking. Do this for at least a few seconds. “Launch” it! There are several different methods for “launching” your rocket: A popular and effective one is to throw the bottle high up into the air and let it fall on to the ground (preferably hard ground, like cement). This is the best method if you're worried about getting hit by the rocket, as you can throw it far away from you and even run in the opposite direction. Another method is to throw the bottle at a side angle so that when it hits the ground, the ground knocks off its cap. Yet another method is to throw the bottle at more of a 90-degree angle, cap-first, on to the ground. Try again. You can skip this step if your rocket works right away. If the rocket doesn't go off when you throw it, pick it up and try unscrewing the cap a little before throwing it again. Just be careful not to unscrew the cap too far, otherwise you're likely to end up covered in Diet Coke. Enjoy the show. When the bottle hits the ground, its cap should fly off and the Diet Coke-Mentos solution will shoot out of the bottle's opening. This should cause the bottle to fly high up into the air. Depending on how you throw it, the bottle might also bounce around sporadically for several seconds. Side-angle launches generally seem to cause the bottle to bounce low and skid along the ground. Vertical launches (in which you throw the bottle straight up into the air and let it fall to the ground) tend to give the rocket more height as it shoots upward. If the bottle is still full of Diet Coke and Mentos but it's stopped moving on the ground, you can try to launch it again to see if it has any more flight left in it. Clean up after yourself. Once you've finished your experiment, don't forget to pick up after yourself. Clean up any bits of tape or Mentos packaging that might have dropped to the ground as you built your rocket. And pick up the rocket! Clean out the bottle and put it in the recycling bin (or bring it to the bottle depot). Try different amounts of Mentos. The more Mentos, the better the explosion. Experiment with putting different amounts of Mentos into the Diet Coke bottle to see what yields the best explosion. Combine Mint and Fruit Mentos in one cartridge. Studies have shown that Mint and Fruit Mentos yield different explosions. Try mixing them together in one cartridge and adding them to your Diet Coke bottle to see what sort of explosion they cause when they are mixed together. Make a larger rocket. Fill an Empty 4-liter milk jug with 4 liters (2 two-liter bottles) of Diet Coke. Leave enough room at the top to add at least an 8-Mento cartridge. As with the original rocket recipe, stick the Mentos cartridge to the lid of the milk jug, fasten the lid, shake the container to release the Mentos into the Diet Coke, then throw the jug high up into the air and let it hit the pavement hard. Make it a contest. Get together with your friends and each make your own rocket. Set up a flag or some other way of measuring height, and have a judge watch and name the winner. 
Buy 1 2-liter bottle of Diet Coke. Buy 1 package of Mentos. Obtain one roll of masking tape. Buy protective goggles. Find a wide-open space to build the rocket in. Wear appropriate attire. Gather your materials. Cut 2 4-inch (10.2-centimeter) strips of masking tape. Remove 5 to 7 Mentos from the roll. Lay the Mentos on to one of the 4-inch (10.2-centimeter) strips of tape. Place the other 4-inch (10.2-centimeter) strip of tape on top of the Mentos. Cut a 3-inch (7.62-centimeter) strip of masking tape and roll it around your finger, sticky side out. Attach the rolled tape to the top of the Mentos. Fasten the Mentos cartridge into the bottom of the Diet Coke cap. Double tape the cartridge to the cap. Twist the “loaded” cap on to the Diet Coke bottle. Shake the bottle. “Launch” it! Try again. Enjoy the show. Clean up after yourself. Try different amounts of Mentos. Combine Mint and Fruit Mentos in one cartridge. Make a larger rocket. Make it a contest. 