the equal reaction is the momentum of the tip being knocked back as the ball hits it at the end of the stroke.

Might have something to do with the fact that the flipper is still accelerating? It's not contacting at a constant velocity. Might be talking out of my ass, been a few years since my last mechanics class.

Edit: Also, it's easier to think of collisions as preserving kinetic energy, not as "equal opposite force". 2nd law of motion is a force applied to one object, not how two objects interact. It makes sense that positive ke from flipper could exactly cancel negative ke of ball.

The biggest consideration is the hardness of flipper rubbers. The rubber takes 'takes' most of the energy. Rubber can't be too bouncy though. Doing live catches with yellow or red flipper rubbers is usually tough.

But that's not important. If you're live catching, you're getting better as a player. Now keep going! Can you post pass? Do a cradle separation? Do you do dead flipper passes? Forget all the hows and whys, keep getting better.

In that thread, link this gif:

http://killscreendaily.com/media/uploads/live-catch-%5Bthe-addams-family%5D-tumblr.gif

A much better example.

I just assumed that it was that tiny-unobservable-with-the-naked-eye bounce that you get at the end of the coil motion that does it. Like, the ball gets to the flipper JUST as it's bouncing down a bit and that soaks up the momentum.

There is always some slop in a flipper mech. On a normal flip, the flipper will always move beyond the normal "held" position for a split second as the force of the upward motion consumes this slop, before the flipper reverses and returns to rest at the opposite "end" of the slop (grab a held-up flipper and wiggle it; you can feel the slop). It is during this brief period of super-extension that the (initially strong) upward force of the flipper tip will decrease to nothing as the flipper stops at the end of the slop. During this decrease, there will be a point where the force of the flipper's upward motion is exactly equal to the force of the ball rolling down. If you time your flip so the ball contacts the flipper at this exact moment, you have a live-catch. Not magic.

"Flip Here"

lc.gif

Pool balls are the same material with the same density though...this is a ball vs rubber...maybe that's the diff?

Pool balls are a bad analogy because the only forces are the two balls' inertia. A flipper mech provides force one way, but then the other way when the bat reaches the end of travel.

A better analogy would be a person shooting at an oncoming pool ball with a pool cue. They could stroke the cue lightly enough that the oncoming ball would hit and push the cue back, or they could hit the ball hard enough to cause the ball to reverse direction. Or they could hit it just hard enough to stop both dead.

When you do the live catch (and do it absolutely perfectly, such that the ball seems to just stick to the flipper) there is no force transferred to the ball, from the flipper. The flipper actually ~absorbs~ the ball's momentum (kinetic energy). The force of the flipper is not equal to that of the ball. It is negative to that of the ball, and subtracts energy from the ball.

Look at the image that metallik posted above. The thin outline of the flipper, at the absolute highest point of travel. That is where you would want to make contact with the ball when making a live catch. It is exactly as he describes in the post just above the image.

I will try to paraphrase again, maybe it'll make some sense...

The ball hits it in that highest position of the thin outline (it is in that position for the tiniest fraction of a second) and the flipper ~goes backwards~ to it's normal resting UP position (the darker outline, just below). So for an absolutely tiny amount of time, the flipper actually moves backwards. It moves backwards a tiny amount until it gets to it's normal "hold" upward position. That tiny backwards movement is a absorbs the momentum of the ball. The flipper applies no energy to the ball, since it is moving backwards.

Think of the egg tossing game, where you try to catch an egg as "softly" as you can. You want to decelerate the egg by having your cupped hands moving in the same direction as the falling egg by starting a downward movement just before the egg come in contact with your hand, cushioning it while catching.

ahh.. nevermind you got it... I got sidetracked by a phone call before I posted

That's not how physics works, dude. "Taking momentum away" is a force in the upward direction on the ball.

IAMA Physicist, so let me work up a proper explanation with math and shit. I've been interested in working this out for a while, so this is as good a time as any. To the whiteboard!

I see it as doing an egg toss. You touch the ball at its highest point and drop the flipper back with the ball decreasing it's momentum to a safe stop. Not sure if anyone said that already. Yep people mentioned this already. Haha

I would love to see this. This question has bugged me for a long time. I never understood how the flipper moving ups stops the ball but a held up flipper bounces it.

Ok, I have to go out (to the local arcade, and then to Guardians of the Galaxy, which just came out here), but I'll take my notebook on the train. I think I've convinced myself, but my notes would not currently convince anyone else...

That's cool. Are you a physicist that can do a decent live catch? That would be even cooler. And kinda important if you're going to explain how one works. Math and shit is cool too, but I'd be much more likely to accept your theory if I know you can break out a live catch when money is on the line. I can do one, but it's no thing of beauty.

note to the Pinball102 folks: have a segment where KME tries to do live catches on a game with no flipper rubbers, superbands, fresh conventional black rubbers, then bouncy white flipper rubbers. I bet there will be both cussing and laughing during the filming of this segment (and a few busted flipper bats!). Would go great with Benny Hill music.

Ask your girlfriend if a car is moving 65 mph how long will it take to go 65 miles.

Have any of you played soccer? If you have or maybe your kids do just think about you stop a soccer ball dead from a teammate's pass (trapping). You hold your foot a bit off the ground and perform basically the same thing as a live catch. You can feel exactly how it works on your foot.

You don't just hold your foot stiffly out, the ball would hit it and bounce off away from you. You turn the inside of your foot towards the ball, with a soft hold so that your foot gives slightly when the ball hits. Cancel out the energy, ball stops.

Just have someone roll you a ball and try it.

Try mastering the drop catch first. The timing of the drop catch isn't quite as difficult to master as the live catch, but will help progress to the live catch. I've got a good handle on the drop catch, but still look silly on occasion when I mistime it and the ball drains like a rookie.

You might also notice that the gif example of the live catch has it rolling down the sling which is a much easier example than a ball coming down the open playfield.

http://killscreendaily.com/articles/pinball-sport-pros-teach-essentials/

Maybe not spot on topic but have anyone had this move work on the pinball arcade video game? I've tried but it doesn't seem to work. Maybe because of the video game lacking the sloppiness of the flippers. Interesting topic anyway how it works on real machines!

A flipper uses energy to change the direction of the ball. When it has reached the end of it's travel, the flipper no longer has enough energy to reverse the direction of the ball. The ball stops, because it transfers it's energy to the flipper mech. Similar to when you see the first ball stop on a newtonian cradle. At that instant in time, its potential energy is zero, and its kinetic energy is greater. Because energy can't be destroyed, the ball's greatest potential energy is equal to its greatest kinetic energy. When the ball hits the flipper, it stops immediately, its kinetic and potential energy back to zero again. But the energy must go somewhere - it transfers into the flipper mech, where much of the energy is lost in the form of heat from friction.
newtons-cradle-motion-24063902.jpg

The flipper hitting the EOS is important otherwise the flipper has too much power and will push the ball up a bit. On poorly adjusted and sloppy flippers you might see this action, where the ball pushes the flipper back a little to actuate full power, thus tipping the ball away.

livecatch_fst.gif

livecatch_slo.gif

Yeah I don't think the flipper physics in Pinball Arcade are very true. The interaction is very binary...short taps on the flippers don't do anything, its either all on or all off, you know?

Yes that must be the case with the video game... No flipper mechs under the table to absorb the energy either. Got pretty clear when I saw the post above concerning the cradle. Would be possible to incorporate though, at least avoid the all or nothing thing.

Can you live catch without flipper rubber? In my mind the answer is yes even if its a bit more difficult...

Pinball FX2 seems to handle live catches and drop catches a bit better than TPA, I'd be really curious to see how they're handling ball and flipper physics differently.

The trick in pinball FX is the ball seems to be made of black matter and weighs as much as a freight train, or the tables are pitched as shown on my TV (ie - about 90° from flat; would love to see banzai run remade with Pinball FX physics, backbox would be spot on)

In PBA the flippers are seemingly powered by railgun coils which rotate the flippers at ~Mach 1.3-1.8, and the balls are obviously hollow.

Both games are quite good at modelling those above mentioned physics, assuming that's what they were going for.

Yes, it would. Even a solid steel ball is elastic to some degree, and a lot of the energy would be absorbed by the elastic compression of the solid metal wall. It will bounce back, just not very much. Make it out copper, bronze or brass and you'll get more bounce, out of diamond or carbyne to get the smallest bounce.

http://en.wikipedia.org/wiki/Young%27s_modulus

Magic

Yes. It's actually easier. The slop or "play" in a flipper mech is the biggest factor to consider here. All brand new parts (or a new game) with bouncy rubber makes live catching MUCH more difficult.

The TOM clip above does in fact show the energy transferred to the ball, but it is VERY subtle. See how the flipper "wiggles" after the catch in the second clip? The more subtle the transfer, the more magical it will look.

Flipper rubber makes a huge difference. I can LC about 90% with superbands while bouncy PBL rubber I am batting around .250.

Aside from low speed ball handling being very different, I find everything is easier with superbands. I can't LC on command without them. Despite that I'm still not convinced I like them beyond their appearance and durability.

Somebody in the Bay area get Adam and Jaime from Mythbusters to do some high speed video of it and a whole episode dedicated to Pinball Wizardry!