July 2017 Bottle Rocket

It’s Not Rocket Science!… Wait, YES it is! (7/5/17)

Launch a Liquid-Fueled “Bottle Rocket”

MATERIALS:

  • Empty 12oz water bottle
  • Strong tape
  • 3 Pencils (preferably unsharpened)
  • Plastic bottle stopper or cork (NOT a screw-on cap!)
  • Measuring cups and Measuring spoons
  • Paper towels
  • Distilled white vinegar
  • Baking soda
  • Funnel
  • Adult Assistant
Rocket Assembly

INSTRUCTIONS:

  1. Unscrew and discard the cap of an empty 12oz water bottle.
  2. Create a launch stand for your rocket by securely taping 3 pencils onto the side of the water bottle, making sure that they are evenly spaced. The eraser ends should point upward and rise past the bottle opening by about an inch.
  3. Using a funnel, pour 6-8 ounces of distilled white vinegar into the bottle.
  4. Place 2 Tablespoons of Baking soda in the center of a dry paper towel. Wrap the paper towel around the baking soda and then fold it up to create a bundle that is thin enough to fit through the water bottle’s opening.
  5. Now be sure to grab your adult assistant, and take your rocket assembly outside to a wide open spot!
  6. Squeeze the baking soda bundle just inside of the bottle’s neck.
  7. Push a snug-fitting bottle stopper or cork into the bottle mouth.
  8. Give the rocket a quick shake.
  9. Quickly flip the bottle upside down so it is standing upright on the three pencil erasers.
  10. Back away fast, or prepare to get splashed!
  11. Once your rocket has returned to Earth, you can re-fuel and launch it again and again by repeating steps 3-10!

HOW DOES IT WORK:

Like every object around us, our bottle rocket follows three simple rules of physics. These rules were originally written down by a scientist named Isaac Newton over 300 years ago; and we call them Newton’s Laws of Motion because they describe how an object will move when a force (a push or a pull) acts upon it.

The First Law says that when an object has no forces acting upon it (like an empty water bottle sitting on a table) it will never move all on its own, but remain at rest (like when we pick up the bottle, or knock it over!). On the other hand, an object that is already moving will continue to move in a straight line until a force causes it to stop or change its direction (like how gravity, wind, or resistance from the air influences our bottle rocket’s flight).

The Second Law says that objects of higher mass (that is, heavier objects) require more force to get them to move than do smaller objects. In the case of our bottle rocket, the force that makes it blast off comes from a chemical reaction between the distilled vinegar and baking soda. This reaction is the same one that makes foamy lava in the well-known volcano experiment because it produces a lot of Carbon Dioxide gas bubbles. Since the Carbon Dioxide gas is contained within the bottle rocket, pressure will continue to build up until it is strong enough to actually push out the bottle stopper. But consider this: if we used a larger (heavier) bottle for our rocket experiment, but still had the same amount of pushing force from the Carbon Dioxide, would you expect the rocket to fly as high? Why not?

The Third Law says that for every force, there is another force of equal strength and in the opposite direction. In other words: For every action, there is an equal and opposite reaction. For our rocket’s flight, it is easy to see that there is a lot of action (force) pushing downward from the tail-end of our rocket. But it’s less easy to see that this same exhaust flow creates an upward push on the bottle itself, a reaction force that is called thrust. If we had not flipped the bottle upside-down before it blasted off, the exhaust would have escaped upward and our rocket would have actually flown down toward the ground!!!

THE MORE YOU KNOW:

Around the 4th of July, some people like to launch fireworks from their backyard. These commercial fireworks are actually low-grade explosives that would be very dangerous if they exploded at ground level. That’s why fireworks are equipped with a solid-fuel combustion rocket to launch them high above the spectators before safely setting off the gunpowder mortar.

GOING ONE STEP FURTHER:

  1. According to the imaginary laws of Chromodynamic Flight Theory, the more attractive that a rocket is, the higher it will fly…so thoroughly decorate the body of your rocket before launching!
  2. Add a nose cone to the tip of your rocket to make it more aerodynamic (able to move through the air). Try using different materials to create the cone: a paper cone, a cone made from play-dough, or an ice cream cone. Which cone works the best?
  3. Add stabilizing fins to your rocket’s body. Try using different materials to create the fins: cardboard, construction paper, or even paper streamers!
  4. Experiment using different amounts of baking soda and vinegar to achieve the highest possible launch. Or use a different bottle size for your rocket body.

3…2…1…blast off for rocket science!!!