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Independence Day is upon us, and one of the best things to do on the Fourth of July is to go see a fireworks show. Fireworks come in all different shapes and colors, and that’s what makes them fun to watch. Before we get to see them explode, though, they have to shoot up into the air on powerful rockets. People who work with fireworks are called pyrotechnicians, and they have a dangerous job that requires a lot of training. Fortunately for us, there’s a way to make safe and simple rockets at home. They’ll obey the same laws of physics as the ones attached to fireworks (or spaceships, for that matter) without the dangerous chemicals and fire that makes that kind of rocket go.
Materials
- A plastic sports bottle with a pop-top (the kind that pops open and closed)
- A jar or cup big enough to fit the bottle into
- Water
- Alka-Seltzer tablets (generic works, too)
- Tape
- Safety glasses
Process
- Find a nice flat patch of grass on a sunny day. Since you’re shooting rockets, you’ll want to do it outside.
- Put on your safety glasses, just in case. This rocket will be spraying water mostly, but it never hurts to be safe.
- Place your jar or cup on the flat patch of grass.
- Unscrew the pop-top from the sports bottle and fill the bottle halfway with water.
- Take an Alka-Seltzer tablet and break it into pieces small enough to fit inside the opening of your water bottle.
- Drop the pieces of the tablet into the bottle and work as quickly as you can to screw the lid back on. Close the pop-top, shake it up, and put it into the cup upside-down, with the pop-top facing the ground.
- Step back and wait.
- How high did your rocket go? Try it out again with more or less Alka-Seltzer to see how the experiment changes.
Summary
Alka-Seltzer tablets are called effervescent because when they begin to dissolve in water carbon dioxide gas is released, which is the fizzy bubbles you see. This is due to a chemical reaction that’s similar to another one you might have done before where you make a volcano with baking soda and vinegar. In fact, this rocket would work with baking soda and vinegar, too, instead of Alka-Seltzer and water, but it would be a lot messier and harder to work with.
People take Alka-Seltzer as a medicine by dropping a tablet into a cup of water, waiting for it to dissolve, and then drinking the fizzy water. In a cup, with a big, wide opening at the top, the carbon dioxide escapes and mixes with the air. When you closed the pop-top on your bottle, though, you cut off that escape route. Instead of slowly escaping, that carbon dioxide had nowhere to go so it built and built and built, creating pressure inside the bottle. Eventually the pressure was so high that it popped the top open and shot out the opening.
The famous scientist Isaac Newton came up with three basic laws of motion, and his third law says that “for every action, there is an equal and opposite reaction.” This means that when a thing pushes on another thing, the second thing pushes back. When you go swimming, you push on the water, and it pushes back on you, and that’s how you move forward. Your rockets work the same way! The carbon dioxide and water that escape are pushing down on the ground, and the ground pushes them back up with an equal force. Since the Earth is way heavier than the bottle, that makes the bottle shoot up into the air! The rockets that power fireworks (and space ships) are a lot more complicated and a lot more dangerous but they work according to this same basic principle: for every action, there is an equal and opposite reaction.
Want more Saturday Science? See all of our at-home activities on the blog or Pinterest.
