November 8, 2014
I decided to take a second look at the speed of a dart coming out of a nerf gun. In this experiment I used photogates to time how long it took the dart to cover a short distance.
Episode 12: Nerf Gun Dart Speed–part 2
When I analyzed nerf dart speed six months ago, I measured the dart launch using some high speed video. You can find that episode here. I came up with around 19 m/s. This go round I used photogates to time how long it took the darts to cover the first 10 cm. I then discuss how certain (or uncertain) I am about the measurement. That is called uncertainty. Even though it sounds weird, I am actually more “certain” or confident in my measurement in this experiment than I was before. Partly that is because I have a lot more data (30 trials shooting the darts) but because I checked it with a radar gun and against some high speed analysis my student did.
Check it out:
Here is my nerf gun:
Uncertainty is a topic I usually save for my AP Physics class, but it seemed like I should include a little in this episode. It really is at the heart of every measurement we make. Here is a site that does a pretty good job explaining the basics if you want to know more.
I was pleasantly surprised that my radar gun could track the dart and that it agreed nicely with the photogate data. That added to my confidence in the photogate measurement.
A Student’s Data
One of my physics students (Derek H) did a project on finding the speed of his nerf dart gun. He used a high speed camera shooting at 240 fps and Logger Pro to determine the firing velocity. He got some good data:
If you are interested, here is his video: Derek’s nerf dart video
I was shocked when I saw that his results were practically identical to mine!…and Derek wasn’t using the same type of nerf gun. That has to be partly coincidental. Physics Professor/Blogger Rhett Allain did an analysis and got a much slower velocity from his nerf gun. Here is his post about it.
I was also surprised that Derek’s results were a lot more consistent too; his uncertainty was more like +0.5 m/s. So, nice job Derek and thanks for letting me use your video and results in this episode:)
If you want to do your own video analysis you can use a free program called Tracker. It does the same sort of thing that the Logger Pro software does. If you have Logger Pro already (mainly educators I would imagine) but don’t know how to do video analysis yet, you should learn–it is an awesome tool for analyzing motion. I made this screencast to help my students. The audio is a little too low, but maybe it can help you get started too.
I have no idea what happened in my last attempt at finding the dart speed. Those results now seems way too high. I must have messed up the analysis. However, I now feel confident in saying that my nerf gun fires at a speed just under 14 m/s which is about 30 mph.
Now go figure out how fast your nerf gun fires! Email me your results.