Gallery Supersonic ping pong ball

[BrainEater]

Originally Posted by IRQ Conflict

Try it with a golf ball muhahaha

I can suggest crazy $IIi7 cause I'm miles away.

A golf ball would not move.

This only works because it's a ping pong ball.It's a thrust thing.This is pure physics.

When the vacuum is going it's about a 15 psi differential.A ping pong ball has a diameter of 1.62 inches.That's an area of ~ 2 square inches.15 psi X 2 square inches equals 30 pounds of thrust on an object that weighs 2 grams ! (yea my maths bad but...)

That about 6800 'G's of acceleration.

[IRQ Conflict]

46g for a golf ball which is 23 times as heavy. I'm not sure but the outside circumference is close is it not? So 23 x 15 = 345psi or more properly 2.42 inches of mercury.

For you to get a golf ball to do roughly what you did with the ping pong ball it would take compressed air @ 345psi or a vacuum @ 2.4in mercury @ 0c. To get it supersonic, well that's a whole other ..ahem ball game.

I was thinking, we could rent one of these for an hour.

[BrainEater]

Ah shitballs !!

My Vacuum pump is only doing -0.75 bar right now......that ain't good enough.

The vacuum thang is very important in this experiment.The terminal velocity of a ping pong ball is really slow.Low mass , high drag.......The only way it'll go 500 mph is in a vacuum....

The vacuum pump is going in for service monday , but really it's not good enough......it's right on the cusp.......The first shot I did that worked was -0.82 bar.For this to work properly you really want -0.99 bar.

I'm messing aroung with making ABS c-d nozzles.

[IRQ Conflict]

I dunno. Maybe the trusty potato cannon would be a better/funner project?

Edit: I tried converting barometric pressure to inches of mercury with negative values. If you'll forgive the pun, it doesn't seem to add up. -0.75 bar = -22.15 inHg ?

Isn't vacuum better expressed as a positive rather than a negative? My brain doesn't want to go there I guess.

[Father Fuzzy]

Not sure what your doing Braineater(as usual)

but you got my interest(as usual)
Subbed!

[Bungwirez]

this project appears to require more suck... and less blow.

[IRQ Conflict]

Oh yeah! Bring on the punishment!

[BrainEater]

Originally Posted by IRQ Conflict

I dunno. Maybe the trusty potato cannon would be a better/funner project?

Edit: I tried converting barometric pressure to inches of mercury with negative values. If you'll forgive the pun, it doesn't seem to add up. -0.75 bar = -22.15 inHg ?

Isn't vacuum better expressed as a positive rather than a negative? My brain doesn't want to go there I guess.

Yep......looks about right.

Bars are a depreciated unit , we're not supposed to use that unit anymore , it's just that it's how a lot of vacuum equipment is labled.

1 Bar ~ 1 atmosphere at sea level on Earth...
It's 14.5 psi and /or 29.5 inHg.

-1 Bar is perfect vacuum......so like -30 inches of mercury.....



ps :

Originally Posted by Bungwirez

this project appears to require more suck... and less blow.

Absolutely.The pump is sucking at sucking !

[clshades]

a perfect vacuum is only theoretical anyway... -.99 will do donkey :)
What you need is a quick release valve on the back end so you don't have to keep taping it. I would suggest solid core ABS too that cellular stuff is garbage... either that or use steel or copper pipe :)

I have access to a threader if you need.

-speaking of which we should run a pipe for your BBQ and turf the propane tank ;)

[Stukka]

The solid core ABS clshades is talking about is called abs dwv. You may or may not be able to find it at home depot though.