Recent content by marietta_ken

I'm trying to design a simple torsion spring catapult to launch a 0.15kg ball at a velocity of 35 m/sec at the moment of separation. The ball will be in direct contact with the unrestrained end of the spring. As a starting point, I'm planning a 0.3m length for that "arm" end of the spring as...

Does the fact that the spring/plate assembly has much greater mass than the ball come into play. In other words, if you take the same amount of KE that exists in a massive spring/plate assy and transfer (a high %) of it to the ball, will the ball not react more "explosively?"

Please forgive my ignorance on what may be simple topics for most of you. I'm just trying to get my head conceptually around a ball launching pet project I'm fiddling with. If you take a rubber (tennis) ball, say of 5 oz mass, and blast it with a sprung plate moving at 70 mph, will the ball...

Thanks a ton for all the help, guys. I did acutally convert to the SI values as mgb and miraculously (sigh, so simple) got the same result. Now the part that is freaking me out is the additional force it's showing I'm going to need if my spring retractor/plunger take that mass up to around 20...

Wow, so is this really saying I'd need almost 19K lb/in for the spring constant?

Thaakisfox -- wow, thanks for spelling it out for me. Using your resulting equation, I got the same # as I did with mgb's suggested cons of energy approach. k=mv^2/l^2 v desired 1232 in/s 70 mph m 0.3125 lbs 5 oz x 5 in k= 18972.8 Not to be a complete moron, but...

mgb -- using the conservation of energy equations I get double (18972.8) the number of previous calc. What gives?

mgb -- yes, I understand that k is a force/length unit. The problem I'm having is that I believe the equation above, when used with the units (lbs, inches and s) I've shown, reduces to something like lbs/sec^2. What am I missing?

Thanks, Chris. I'm still confused on units, however. With a couple of conversions to get matching units, my parameters are: v desired 1232 in/s m 0.3125 lbs x 5 in Based on the equation k=v^2*m/(2*x^2), I get: k = 9486.4 ??Units? Or, do I need to put something else in diff...

Could one of you mechanical geniuses please help out a dumb ol' elec engr? I've searched the boards for a few hrs now, but can't seem to get confidence in my answer to what should be a simple problem. I'm trying to build a simple a simple tennis ball launcher to fire a ball out at 70mph --...