New Research Project: high velocity projectiles with small masses

[Alumen]

Hi everyone, I am new to this forum. I am a high school student but I am extremely interested in science and I like to call myself a "junior physicist". even though I am not nearly as smart as a real one. But I suppose I am working my way up there. I am hoping to go to college and get a degree in Physics engineering if that is possible. As I have a huge passion for both subjects.
Me and a friend are starting a new research project hosted by the school science club.For now it is just us working on the project.

We are going to do research on high velocity projectiles with small masses. We are attempting to get a small projectile(literally tiny) at speeds faster than sound. Will be testing impact phenomena on different substances. Hoping to get something interesting out of it. To get the projectile at this velocity we are probably going to use something along the lines of a small light gas gun. We do not need the projectile to get to mach 7 like the real ones but we think it is doable to break the sound barrier.

Overall does it sound interesting or completely boring and a waste of time? I think it would be neat to test the different shock waves on substances like water and metals. And who knows, this is physics so I am sure we will get something out of it that we would have never predicted.

 

[Vorde]

Being someone in a very similar position to you, I can tell you that your project definitely sounds like an interesting one that could produce some very interesting and fun results. Also I've been told several times by my guidance counselor that doing projects like that both looks really good to colleges and gives you valuable experience, if I were you I'd definitely continue with that, looks quite fun!

 

[Alumen]

Great! I will certainly continue this project then. My teacher gave me permission to use the lab at school. So I will have a good place to work.

Does anyone have any idea how to measure the velocity of this? It occurred to me that it will be relatively hard to measure something so small going at such a high velocity. But I know it is possible!

 

[Vorde]

I don't have enough experience with them to tell you whether or not radar guns are useful at that size/speed, but it's certainly worth a try.

If they do not work, you could devise a method to tell when to projectile hit the target (highish speed camera for example-any decent quality one might work) and simply apply
V=\frac{Δd}{Δt}

 

[Alumen]

Radar gun sounds like something I need to research. Like you advised, I could easily use the kinematics to figure it out, but I would need to know at least two variables. Probably time and displacement. I suppose I could measure that at long ranges. Or possibly with a camera like you said.

 

[AlephZero]

You will probably have problems trying to fire a "tiny" projectile at high speeds. Obviously you can fire something the size of a rifle bullet faster than the speed of sound, but the drag force is proportional to the cross section area or length squared, while the mass is proportional to volumne or length cubed. So the deceleration = force/mass increases as the object gets smaller, for the same shape and material.

For speed measurement you could try using a camera with a long exposure time, and a strobe light to make multiple exposures at a known rate on one photo.

Speed of sound in air = 340 m/s, so if your projectile is traveling at say 500 m/s, even with a strobe flashing 1000 times per second it will travel 0.5m between each flash.

You need to think hard about the safety issues. Projectiles don't always go where you aim them if they are aerodynamically unstable, the target might shatter with pieces flying around in random directions, etc...

 

[Bobbywhy]

Alumen, radar guns emit microwave energy which is reflected from the moving target (car, baseball, etc.). Then that reflected energy gets received, detected, and measured to calculate velocity. Now, if you have a really small projectile like a bb, for example, forget about using a radar gun. It has such a small "radar cross-section" that it will not reflect enough energy to get detected. High-speed optical camera is the usual choice for this type of experiment. Good luck!

 

[Danger]

There is also always the old-style foil chronograph. The projectile breaks one conductive ribbon, which starts the timer, then a second one which stops it. They're quite accurate and inexpensive.
As Aleph mentioned, in what I consider an understated manner, this rig could be extremely dangerous or even lethal. Please exercise the utmost caution and have an expert advise you as to safety measures. There might even be legal restraints upon what you can do. (I know that sounds stupid, but here in Canada your device would be legally defined as a firearm which would have to be registered, securely stored, operated by someone with a possession license, etc..)

 

[Integral]

Guys don't worry about generating hyper sonic speeds, yet. Simply measuring the speed of a projectile would be a good project. Start with measuring the speed of a bb or what ever projectile you have. Several methods have been suggested, try them all. Learn about the errors involved and learn how to take good repeatable measurements.

Here's another method, google "Ballistic pendulum"

 

[Alumen]

Trust me, safety is the most important part of this, It will be fired inside of a closed chamber(already made), and won't be firing at anything that can shatter. The projectiles will only be fired at about a 3 foot range. So deceleration is not a huge worry but we will take it into consideration. Also, the materials we are shooting at will be in a cage within a cage. So, things shouldn't fly all over the place.

However, last night while going to bed(lol), I thought of that bullet pendulum idea Integral suggested. It seems easy enough to do, and also easier to measure.
Thanks a lot for the help guys! I will keep you updated!

 

[Alumen]

Today I decided to tone down the power of the gun. It will be simply a little air gun. Still with an ok velocity, but not to much force. And since it decelerates so fast it will not go fast for too long.

 

[Danger]

Glad to hear that, pal. Although I love things that go BOOM, I was a little worried about the safety factors of your original concept. Even with the down-scaling, though, don't give up your goggles and earplugs.