Whenever I lay on my back and toss a a tennis ball, or any other object for that matter, into the air it seems like it’s being pushed away from my feet in an unnatural arc. It’s next to impossible to lay on your back on a flat surface, and throw a ball into the air and have it return directly to your hand - always seems to drift “up” (in relation to your head) as it ascends and descends.
Try it. Is this just a simple optical illusion caused by… something, or should I see a neurologist? Do humans just have screwy visual senses when they’re laying on their backs? It’s not all that hard to stand and throw a ball underhanded into the air and have it come straight up and down - shoot I can even juggle. I’m a relatively accomplished athlete and don’t have any trouble with this kind of thing running around on my feet - just laying on my back.
It’s your brain trying to automatically compensate for gravity. When you throw a ball normally, you instinctively aim high to allow for gravity, but when you’re on your back, throwing the ball upwards, the effect of gravity no long acts towards your feet, so you aim the throw high, in the direction of your head, out of instinct.
I used to lie in bed and throw tennis balls between my left and right hands. If anything the balls would drift down (towards my feet) but mostly they would be level.
Q.E.D., I had thought that the brain would realize “hey, I’m on my back” and compensate, or at least not be surprised or have it feel like some unseen force is acting. Most optical illusions I’m familiar with rely on some sort of “bug” in the brain’s wiring that only works on the 2D level - even the “person-looks-really-big-in-a-small-room” functions in 2D.
If it’s just the brain being confused about the lack of gravity I’d think there’d be a drift toward my head when I intentionally throw one of my balls towards my feet - but there’s not. Could there be some lack in people visually judging arcs or size/distance relationships at work here too?
I have taught people to juggling a few times and seen it taught a lot more. Many people “drift” the balls in or out. So they end up walking forwards (usually)* or backwards to keep up with the plane of the balls. Since that’s standing up, on your back, the misjudgement’s likely to be greater. (While lying down, it’s a right angle to the body, but the plane is the same.) People aren’t perfect.
Most illusions that I’ve heard about fucntion through pretty well established phenomenon - is there any technical term for what the jugglers and I are getting at? I’ve just never heard it discussed before as a studied phenomenon.
You just started this thread to get Dopers to lie on their floor throwing balls and looking silly, didn’t you?
After some experimentation (hope a Koosh ball is an acceptable substitute), I think it’s just harder to coordinate the counter-rotation needed for a straight vertical toss while you’re on your back. When I’m standing up, I toss by just rotating my elbow, and release when my forearm is horizontal. This way, there’s very little horizontal movement. Lying (lieing? laying? Ah, whatever) down, you have to have the elbow rotating one way with the shoulder and/or wrist going the other, so it’s harder to release at just the right moment.
I’m thinking this is more a physical/mechanical phenomenon than psychological. There’s really no illusion, the ball isn’t going straight up, so it lands somewhere other than where it started. If it really bothers you, I’m sure practice would take care of it; I once saw a guy who could juggle three balls while lying on his back.
How many of you who responded actually tried it before typing your reply?
sivispacem what position is your arm in when you are thowing the ball? You couldn’t do it with your arm out to your side and upwards in the typical underhand fashion, because you can’t get your elbow at the right angle this way, so I don’t see how QEDs theory could follow.
At least sciguy is scientific enough to try it out.
How does being forced to alter your throwing style in any way affect what I said? I might very well have been wrong, but nothing you’ve said demonstrates that.
just tried a few methods of throwing the ball into the air, it usually arced as i expected ( straight accross my chest/ straight up and down), the only way i could get the ball to arc towards my head or my feet was to throw the ball in un-natural ways.
Thinking about it ( tries some more experiments… )
If i throw the ball as i would juggling(underarm style elbows at sides) it arcs towards my head (specifically my face). i think its a mechanical thing, as it would be quite hard to release the ball soon enough to launch the ball perp. to your body so that you can catch it with anything other than your mouth or eye socket.
<off topic> ftg or scarlet67. I need help, i’m trying to juggle, but recently i’ve found myself spinnig on the spot, as my right arm is (i think) trying to throw the ball further over than my felt arm is throwing them back. I used both the wall and bed tricks to get the balls travelling right before, but now that i’ve stopped throwing the balls in front of me, i seem to spin myself anti-clockwise( i really am naff at explanataions). any neat tricks you can think of for overcoming that?
</off topic>
Okay so Q.E.D. seems like he might know his balls better than anyone else - but I’m still wondering if there’s some deficiency the human brain has in interpreting parabolas/arcs that would cause an illusion.
Like when you’re in an airplance everything really seems like it’s teeny and you could walk around like Godzilla, the brain has trouble dealing with the distance/size thing so you can do some neat illusions with that. Maybe there’s a similar mechanism going on here.
I’m going to play with my balls some more and see if I can figure this thing out - I hope more Dopers join me!!
I noticed it’s really easy to get the ball to go stright up and down when you throw the ball without any spin. Sort of thrust your hand upwards and open your hand like a shot put, instead of throwing it like a baseball.
Up and down with the basbeball throw is suprisingly hard. Mine drift “downwards”. I think if you could really wind up and get some room behind you to throw upwards (somehow), and with a little practice, it wouldn’t be that hard.
I was thinking about this a little more (I am amused by simple things), I think three things are responsible for this:
The mechanics of throwing a baseball-style throw upwards while lying on your back are awkward, with the wrist needing to be cocked more so and the lack of space behind/under you to use to throw.
The 3D thing you mentioned. Judging from only the z-plane is naturally tough, whereas tossing underhand while standing uses a mixture of xy and z planes. Why is it tough? See #3.
