Bottle Rocket

We may imagine an old classroom with formulas written on a chalkboard when we think of physics. But this doesn’t need to be the case! Sometimes we’re able to perform exciting experiments to learn something! There are many things we can do to learn that aren’t just memorizing equations; you can get outside and understand concepts by seeing them happen right in front of you.

A bottle rocket is a fun home project that is a great way to demonstrate how Newton’s three laws of motion work in real-world situations.

Bottle Rocket Explanation

It is simple to build a bottle rocket, and you can follow along with this article to build your own. First, we will need the items listed below:

• One plastic bottle, approximately 60 ounces, would be best.

• One cork that will fit tightly into the entrance of the bottle.

• One pump with a needle adaptor, with a long line to minimize danger.

• One sheet of cardboard, alongside something to cut it, and stick it together.

• Water.

Next, we need to use our list of items to assemble the bottle rocket. The instructions are listed below:

1. Take your cardboard and cut out some side fins. You will need up to five but no less than two. Stick them onto the side of the bottle. You want them close to the cap. It is important to stick the fins onto the bottle so that they’re an equal distance away from each other. For example, if you were using two fins, you would want them to be on opposites of the bottle. You may also want to fashion the fins so that the bottle will stand up on its own

2. Take the remaining cardboard, and fashion a cone out of it by cutting out an isosceles triangle with the two identical sides shorter than the final side. Stick both of these sides together, and then stick the entire thing onto the side of the bottle without the lid, with the point of the cone facing away.

3. Take the cork and the needle adaptor end of the pump, and carefully put the needle through the cork. Make sure you see the tip of the needle on the other end of the cork, as it needs to pierce it clean through.

4. Remove the lid of the bottle, and fill it with water. Aim to fill the bottle up to about a quarter of the way filled; you may want to add more after using it a few times.

5. Take the cork, now pierced with the needle adaptor, and push it into the hole in the bottle, making sure that it is a tight fit and won’t budge easily.

6. Make sure you have an area with a lot of open space in every direction, such as an open field or an empty parking lot.

7. If you made your fins so that the bottle can stand on its own, do this. Otherwise, place the bottle rocket in a way where the tip of the cone will face the sky, possibly through the assistance of another item to hold it up.

8. Carefully pull the pump away from the bottle rocket, being sure not to knock it over.

From here, we are ready to use our bottle rocket! It should look something like this, although it is ok if your bottle rocket differs slightly:

One example of a bottle rocket. Note that yours may look different, depending on how you customized it.Wikimedia Commons

To use the bottle rocket, pump air into it until the bottle rocket suddenly flies away! Hopefully, you get it high into the air!

What are the Forces that a Bottle Rocket Experiences?

So, why does the bottle rocket take flight when you fill it full of air? When you pump, you add more air into the bottle while the bottle still has the same volume. By doing this, you’re increasing the pressure inside the bottle, which is exerting a force on the inside of the bottle. Eventually, when this pressure becomes too much for the bottle to handle, its force will push on the cork enough to rapidly eject it from the bottom of the bottle.

The sudden release of pressure due to a new opening in the bottle will push all of the air out of the bottle as quickly as possible. When the air exits the bottle, it pushes out all of the water alongside it, with the force that was previously pressurizing the bottle. With the water moving at this velocity, it will, in turn, provide this same force in the opposite direction to the bottle, causing it to fly up with a force equal to the force exerted on the water.

The fins and cone we added to the rocket act as stabilizers, keeping the rocket in the same position as much as possible, achieving a uniform flight path. They also help to minimize air resistance, allowing the rocket to fly even higher. These reasons also explain why we need to space the fins equally apart. If they were uneven, one-half of the rocket would have more fins on it, making one-half weigh slightly more. This causes instability and will prevent the bottle rocket from moving straight up. Instead, it will move in the direction the heavier side is facing.

This diagram shows the forces that a bottle rocket will experience as water is expelled from it, as well as labels showing where everything on a bottle rocket should be.Science World

Bottle Rockets and Newton’s Laws of Motion

This bottle rocket project will demonstrate all three of Newton’s laws of motion.

Bottle Rocket Inertia

Newton’s first law shows us that when the bottle rocket is initially at rest, it will remain stationary until a force is exerted upon it. In this case, the pressure released within the bottle is this force.

Bottle Rocket Force

Newton’s second law is shown through both the mass and the acceleration of the water as it shoots out of the bottle. Therefore, the acceleration of the water will be equal to the force exerted by the water divided by the mass. Because of this, if we add more water, we can potentially increase the distance the rocket travels, as adding more water means increasing our value of mass, which will, in turn, increase our value for force. The formula looks like this:

\[a=\dfrac{F}{m}\]

Bottle Rocket Action and Reaction

Another example of a finished bottle rocket, this time decorated! This one has the lid at the top and the bottom cut out instead, but it will work the same way. Pinterest