Science Buddies: "Ask an Expert"

Hello,

I am a student participating in my school's science fair. My project is: Does a rocket's shape affect its travel? If so, what's the best structure?

I plan to build 6 rockets with 3 different fin types and 2 different fin placements out of heavy duty paper. (Elliptical, rectangle, and parallelogram with 3 and 4 fin placement.). How does each fin and fin placement work? How does it help the rocket fly? Does fin placement matter?

The way I plan to test this is by making a PVC pipe launcher with an air compressor. I plan to launch it upwards, but if I do so, I do not know how to measure how high it goes. I will also observe how it flies. How should I measure it? Or should I just launch it horizontally, which makes it easier to measure, but that's not how real rockets work.

Any information you can share would be greatly appreciated.

Thank you,
Gianna

Hi, Gianna!

Fin placement and fin shape definitely affect the rocket's ability to fly. These factors can affect something called drag force, which can slow down the rocket. Typically, you want to place your fins as far back on your rocket as possible so your rocket can be stabilized. Although this is for water bottle rockets, here's a link to how fin size and placement can affect your rocket:
http://www.water-rockets.com/article.pl?121,0

As for measuring how high your rocket flies, you can simply measure the amount of time it takes to reach its peak height! Then you would use the following equation:

d = (1/2)at^2

D stands for distance traveled, a is acceleration due to gravity (9.81 m/s^2), and t is time. Plug in time and acceleration, and you should get the height that your rocket traveled to! Let me know if you have any questions

Hi Gianna!

In addition, for determining how "well" your rocket flies, you could film it using slow-motion so that you can make observations; although these observations will be qualitative (non-numerical data) rather than quantitative (numerical data), you can still include them in your data section and mention them in your conclusion, even though the time traveled will be the actual numerical data. Hope it goes well!

Elena

Hi Gianna -

You could also use video analysis software and a video camera to record the motion of your projectiles. There are two apps that I am aware of - Vernier Video Physics, which runs on iPhones and iPads. It is a cheap-ish app ($3), but it's quite polished. The other option is a program called tracker that runs on pretty much any computer, but you also have to install Java, and the interface is not as nice as Vernier program (It can do more, though, so there's that). With either program you can analyze a video and determine the path, the velocity and the deceleration of your rockets. Good luck!