Join the science discord! https://discord.gg/pw5sZ3PTye The first 1,000 people to click will get 2 months of Skillshare Premium free: http://skl.sh/backyardscientist

Keep Reading below!
Backyard Scientist merch!! https://thebackyardscient.ist/shop/

Thanks iX Cameras http://www.ix-cameras.com/ and Matt Rece https://www.youtube.com/user/mattrece/videos for helping with the high speed shots!

Giaco Whatever video: https://www.youtube.com/watch?v=BrtBc-9pQv4


A few more thoughts on the Nerf Cannon.
Yes, I know if I used a longer barrel I could get higher speeds, but I did not want to deal with a 20ft long gun. I think a 6ft barrel was enough to show what a supersonic nerf dart can do.

Davekni got a pingpong ball going 2000mph which is 2930 ft/s!! (mach 2.5). His barrel was 20ft long. It can shoot through 3/4in plywood! You can see that video here- https://www.youtube.com/watch?v=5xuwu4gjNbQ

I always thought the speed of sound was the limiting factor, because the flow 'chokes' at mach 1. Its a big controversy among air-gunners, and theres like a 900 post topic on it here https://www.gatewaytoairguns.o....rg/GTA/index.php?top Some guy got one going like 2100 ft/s which I thought was impossible. https://www.youtube.com/watch?v=qUq4OQqZ2bw So it prompted me to do some research.

It turns out flow does choke at mach 1, but its only the mass flow that chokes. The gas can still expand supersonically.



Also a big thanks to Dr. Carl Knowlen from University of Washington, and u/Overunderrated, u/TheQueq, and u/InductorMan from reddit.





Here are the papers I referenced:

A COMPARISON OF DISTRIBUTED INJECTION
HYPERVELOCITY ACCELERATORS - https://www.researchgate.net/p....ublication/268456817
Probably the most concise and easily understood!


Numerical Evaluation of a Light-Gas Gun Facility for Impact Test
https://www.researchgate.net/p....ublication/270629342
Shows different muzzle velocities for different barrel lengths


THE THEORY OF HIGH SPEED GUNS
http://www.dtic.mil/dtic/tr/fulltext/u2/475660.pdf
Probably the most extensive on the subject "The reader Is assumed to be an advanced student in engineering." I hope you payed better attention in physics that I did.

Outro music by MDK, https://www.youtube.com/watch?v=2_t5Lm040Gw

Fortnite clip from https://www.reddit.com/r/FortN....iteBR/comments/8e7vq