Skateboard Rocket Car
Use a Mentos® and Diet Coke® Geyser to transform a skateboard into a rocket.
Anyone who has tried it will tell you that the Mentos and Diet Coke geyser is totally awesome! Here’s a way to turn the explosive geyser on its side and transform it into a horizontal rocket motor that powers a skateboard over the ground.
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- ** Supplies available in the Soda Geyser Car Kit **
- 2-liter bottle of diet soda (You’ll probably buy much more later.)
- Roll of Mentos mints
- Duct tape
- Skateboard (Use one of your older skateboards because of the mess you’ll make, or your friend’s new skateboard would be fine.)
- Steve Spangler’s Geyser Tube®
- Safety glasses
Find a safe and suitable launch site for your Skateboard Rocket Car. Empty paved parking lots or paved driveways work as great launch areas.
You’ll need to attach the full soda bottle to the skateboard so that the geyser has a clear shot backward. Make sure there is plenty of room behind the geyser because when it launches, it will really take off!
Check out the design of your skateboard. If the skateboard tips curve up on the ends, the geyser might be deflected and the skateboard won’t move much. You may need to add some layers of cardboard between the soda bottle and the skateboard so the rocket “exhaust” clears the tip of the skateboard.
When you’ve got the bottle placed just the way you want it, have your helper hold it tightly as you wrap the duct tape once around the lower end of the bottle and the skateboard and then once around the top end of the bottle and the skateboard near its tip. Now that the bottle and the board are joined together, you’ve made a launching system!
Put the system on the ground and check the alignment of the bottle with the skateboard. It should be straight and centered, and the open end of the bottle needs to be above the curved tips of the skateboard. When you’re happy with the placement of the system, wrap two more layers of duct tape around each end of the system right on top of the
first layer. Any color of duct tape will do, but even scientists need to let their inner expressive selves loose sometimes. Be daring!
Hold the system off of the ground, keeping it vertical, with the top of the bottle pointing up. Remove the bottle cap. Now you’re getting serious!
Ask your helper to open one end of the Mentos package and loosen the mints a little so they can slide out easily. Have your helper hold the mints in one hand and place the open end of the Mentos package above the opening of the bottle (or trade places and you do it). Then, lift the package straight up and slide all of the Mentos mints into the soda all at once with the other hand. Do this by pinching the closed end of the wrapper between your fingers and sliding the mints toward the open end. This will push the Mentos quickly into the bottle in one continuous motion. Note: It is essential, but tricky, to drop the mints into the bottle all at the same time. If they don’t fall into the bottle at the same time, the reaction will start before you’re ready and your Skateboard Rocket Car may take off too soon! Skip ahead to the “Take It Further” section to solve the problem using Steve Spangler’s Geyser Tube® launcher.
There’s only a split second to set the system on the ground before the geyser erupts and shoves the Skateboard Rocket Car downrange. Once the Mentos drop into the bottle, place the Skateboard Rocket Car on the ground as fast as you can and get out of the way! If you hesitate, you’ll get a tasty but very messy shower and then, aw shucks, you’ll have to do it again.
How Does It Work
Soda pop basically consists of lots of sugar (sucrose, fructose, or a diet sweetener), some flavoring, water, and preservatives. What gives soda its bubbly appeal is invisible carbon dioxide gas (CO2), which is forced into the liquid using tons of pressure. Until you open a soda, which makes lots of room, the gas mostly stays suspended in the liquid and can’t collect to form bubbles, which is what gases naturally do. Even when the bottle is open, however, most of the gas stays in the liquid and provides the fizziness of the soda. However, if you shake the soda and then open it, the gas is quickly released from the protective hold of the water molecules and escapes with a whoosh, taking some of the liquid along with it.
There are other ways to 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. Also, compare the foaming of diet soda to regular soda when each is poured over ice.
The Mentos Secret
The reason why Mentos mints work so well is twofold— tiny, very tiny, pits on the surface of the mint and the weight of the mints themselves. Each mint has thousands of micro-pits all over its surface. These tiny pits are called nucleation sites, and they’re perfect places for carbon dioxide bubbles to form. As soon as the Mentos hit the soda, bubbles form all over the surfaces of the mints and then quickly rise to the surface of the liquid. Couple this with the fact that the mints are heavy and sink to the bot- tom of the bottle and you’ve got a double whammy. The gas released by the Mentos literally pushes all of the liquid up and out of the bottle in an incredible soda blast. The geyser continues to erupt as long as the pits remain on the surface of the mints. Eventually, enough of the surface is dissolved so that it becomes too smooth for the gas to rapidly collect. At that point, the reaction slows and stops.
Use a magnifying glass to look closely at the surface of a single Mentos mint and compare it to one that has been dropped into diet soda. You might be able to see the tiny pits on the surface of the new mint. The tiny pits are the key to all of the soda geysers you’re going to make now and at every party you go to in the future. You’ll be the most popular person at the party!
Physics in Motion
The Skateboard Rocket Car is also a great example of physics in motion. Sir Isaac Newton, an English scientist, writer, philosopher, mathematician, and more, discovered some laws of physics way back in the late 1600s and early 1700s. In a word, he was really smart! In order for anything to move, it must obey Newton’s Laws of Motion, and there are three of them.
Simply stated, a Skateboard Rocket Car standing still will remain standing still; a moving Skateboard Rocket Car will continue moving in a straight line. These conditions don’t change unless an outside force is strong enough to make the system move faster or slower, stop, or change directions (that is Newton’s First Law of Motion). Not too complicated, right?
Newton’s Second Law says that to cause the system to move faster or slower, stop, or change directions, the force used has to overcome the inertia (or motion) the Skateboard Rocket Car already has. Okay, this is getting a little more complicated.
And for the big finale, Newton’s Third Law of Motion states that for every action there is an equal and opposite reaction. The force of the soda geyser whooshing backward out the bottle is exactly matched by a force pushing the Skateboard Rocket Car forward. The stronger the backward geyser, the faster the car moves forward—that is why the Geyser Tube creates a more powerful launch.
Who knew physics could be so much fun?
Take It Further
The Skateboard Rocket Car is an activity you (and your now diet soda–soaked adult helper) will want to do over and over. Perform the activity again using a different variable—a different brand of diet soda, a different type of soda (regular instead of diet), a different sized bottle of soda, a different type of mint, or a different skateboard. The options are endless, so keep experimenting, all in the name of science . . . or just because it’s really fun!
To make the launch sequence simpler, cleaner, and more consistent, you could use Steve Spangler’s Geyser Tube® launcher (available at www.SteveSpanglerScience. com). With this device, dropping the Mentos into the bottle is the same every time, and its design also intensifies the blast. The designers of the Geyser Tube shared this secret: this special device does more than just drop the mints into the soda. The special design utilizes the Venturi effect to maximize the eruption of the geyser. The Venturi Effect is similar to placing your thumb over the end of a garden hose that’s shooting out water. The velocity of the water outside the hose will increase when you decrease the size of the opening. The same thing happens when you use the Geyser Tube on the Skateboard Rocket Car.
You can compare the performance of your Skateboard Rocket Car with and without using the Geyser Tube. Use chalk or tape to mark the starting line on your driveway and then launch one original Skateboard Rocket Car and one turbo Skateboard Rocket Car (using the Geyser Tube). Make sure you keep all other variables the same. The only difference in your Skateboard Rocket Cars should be the use of the Geyser Tube. Measure the distance of the launches and compare the data. Chart your data, write up your discoveries, and you have an “explosive” and awesome science fair project!
Adult supervision is required because there’s going to be soda flying everywhere. If you’re an adult doing this, the good news is that diet soda isn’t sticky, and it’s easy to get off your neighbor’s car.