Air Trajectory B/C

[phoebecaulfield]

Hi guys, could I please get some advice on our design?
We made a simple quasi-piston design where a mass falls through a vertical pvc pipe so it pushes air through a smaller horizontal pvc which launches the ping pong ball. Our mass (3.5 kg) is pretty much air tight and there seems to be no air leaks between pipe connections, but it's not launching the ball. Either the air just goes out around the ball or the ball is so tight in the pipe that the mass falls slowly.
Does the placement of the ball in the pipe matter? Right now, it's at the very end.
Thanks for your help!

[chalker]

Hi guys, could I please get some advice on our design?
We made a simple quasi-piston design where a mass falls through a vertical pvc pipe so it pushes air through a smaller horizontal pvc which launches the ping pong ball. Our mass (3.5 kg) is pretty much air tight and there seems to be no air leaks between pipe connections, but it's not launching the ball. Either the air just goes out around the ball or the ball is so tight in the pipe that the mass falls slowly.
Does the placement of the ball in the pipe matter? Right now, it's at the very end.
Thanks for your help!

You need some adjustable resistance to hold the ping pong ball back a bit. Something like an o-ring or small piece of tape. You want the ball to be able to slide smoothly past it once it overcomes the resistance.

[retired1]

I think that you need to keep it simple. 1 1/2 schedule 40 PVC pipe is a perfect fit for the ping pong ball. Any burs at the end of the pipe need to be sanded off. The pipe needs to have the bore cleaned of "refuse" periodically. We use a microfiber shop cloth wrapped around a 1" dowel. You repeat this until there is nothing in the tube.
You allude to having joint leaks. Where??

[slapyou512]

So is it okay to blow up my device with a breath? its at ambient pressure because the air reservoir is not pressurized. It only takes one breath to fill my reservoir, I just wanted to double check that its okay to do this before launch

[chinesesushi]

So is it okay to blow up my device with a breath? its at ambient pressure because the air reservoir is not pressurized. It only takes one breath to fill my reservoir, I just wanted to double check that its okay to do this before launch

I believe it has been mentioned before that as long as you can show that the reservoir is open to the atmosphere, it should be at atmospheric pressure no matter what you put into it. If anyone gave provide a website/link/physics/etc. that could back this up maybe that could serve as "verification" at tournaments XD.

[mej710]

So under "construction" in the event manual, it says the triggering device "must extend out of the launch area, allow for competitors to remain at least 1m from the launch area, and does not need to return to the launch area after launch." When is says "does not need to return to the launch area" are they referring to the triggering device or the competitors? I'm wondering if we are allowed to return to the launch area between launches to put our mass back to where it was at the beginning of the first launch.

[retired1]

They are talking about the firing device. Many people will attach a lanyard to a pin the when pulled out will drop the load.
Obviously, you have to go back to the device to reload and re aim/adjust.

[mej710]

Ok great. We were thinking of making our device with two pistons. Something like this: https://www.physicsforums.com/proxy.php ... ed2d5ce7ff
Is anyone else doing something similar? If so, what are you using to make the pistons?

[zarnold16]

I have read the rules at least 3 times. Can I do a catapult like design or what is a good way to make one like a stomp rocket.

[iwonder]

I would suggest that you read rule 3.b. a 4th time

If that doesn't answer your question, how does a catapult create air movement or pressure that's used to move the projectile?