Slinging.org Forum - Some conclusions from a picture

Yurek

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Some conclusions from a picture
Apr 22^nd, 2006 at 9:34pm

Today me and my son spent some nice time outdoors. When I was slinging balls for our dog Smyk, he took a few pictures of me. One of the photos is great, the boy has caught the dog-ball just after the release. Thus I had an opportunity to make some interesting calculations.

The camera set the shutter at 1/320 s (I believe it is a very accurate setting). In this time the ball was drawing the light trail on the picture. So only thing I need to calculate the velocity, was the length of the ball relocation in this time. It was very easy to calculate it from the picture.

I precisely measured (mm) the length and width of the trail on the zoomed picture on the screen. Then I was able to calculate the ratio:

length/width = 82/27 = 3.04

Since the width = the ball diameter = 0.068 m, there was no problem to calculate the length of the trail:

length = 3.04 * 0.068 m = 0.21 m

In order to get the length of the ball movement:

s = length - ball diameter = 0.21 m - 0.068 m = 0.142 m

Finally, the dogball velocity is

v = s/shutter speed = 0.0142 m/(1/320 s) = 45.44 m/s

v = 164 km/h = 149 foot/second = 102 mph

So, the kinetic energy of the movement is

E = mv^2/2 = 0.04 kg * (45.44 m)^2 = 41 joules = 30 foot pound-force I'm curious, how it could be felt by our heads Shocked

Consider, the real velocity could be a bit bigger, because of a possible 'diagonal' camera position relative to the trajectory. Anyway, the result is surprising considering, that it was just easy slinging for fun with the dog, using a big soft and light weighted (ca. 40 g) squealing ball, and the relatively short sling. Even, I don't remember if that shot was a good one.

The next interesting thing on the picture is, that you can see the spiral trails of the color dimples from the ball.

It looks like in this case the ball had the "point-first" fly ??? At my guess, the ball is doing ca. 1/8 (or more) of the full rotation, in the time 1/320 s. It gives:

(1/8)/(1/320) = 320/8 = 40 rotations per second = 2400 r/minute !? Damn! It is faster then usually electrical engines do. Or maybe I'm wrong in the calculations.

Just enough the numbers. For the end, here is the picture of the Smyk among the fresh spring grass, just after a refreshing bathing. He deserved it for helping during the experiment.

Jurek

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In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.

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siguy Interfector Viris Spurii Offline si vis pacem para bellum Posts: 1714 connecticut Gender:	Re: Some conclusions from a picture Reply #1 - Apr 22^nd, 2006 at 9:41pm that is some pretty good data. sounds like you guys had some fun.
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Johnny Funditor Offline Posts: 620 Goodlettsville,TN Gender:	Re: Some conclusions from a picture Reply #2 - Apr 22^nd, 2006 at 10:05pm Yurek, Are you a physics major? Those are some pretty interesting numbers! I think you can sling that ball at 102 mph..! Johnny
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Tint

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Re: Some conclusions from a picture
Reply #3 - Apr 22^nd, 2006 at 10:42pm

Amazing pictures and calculations, Jurek!
Thaks for sharing.

I never doubt that you can throw a object over a hundred miles an hour with ease.

What suprised me most was the angle of the sling cords and your arm at the point of release. Your arm was almost horizontal, the pouch of the sling is located way infront and yet the ball was still traveling upwards! I still don't quite get it. I thought the position of the release would have to be almost directly above your head for this kind of shot....... Embarrassed

Pete Sampras could serve up to 130 something miles/hour with 5000+ rotation/min on the ball on his first serve and 110 mile/hour and 8000 rotation/min on his second serve. But that's Pete Sampras going for full power. Considering it was just a casual throw playing with Smyk, YOU REALLY ROCK!

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Altay

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Re: Some conclusions from a picture
Reply #4 - Apr 22^nd, 2006 at 11:17pm

So I'm not the only one who slings in their pajama bottoms Roll Eyes

. By the way, what sling style were you using?

Quote:

What suprised me most was the angle of the sling cords and your arm at the point of release. Your arm was almost horizontal, the pouch of the sling is located way infront and yet the ball was still traveling upwards! I still don't quite get it. I thought the position of the release would have to be almost directly above your head for this kind of shot....... Embarrassed

His arm would have been vertical at the point that he let go of the release cord. But you have to remember that he's following through, so if the length of his arm was twice the length of his sling (folded), then his arm would have to be moving 2/3 the speed of the ball. Therefore, his arm would be moving at this speed after he releases the cord, and therefore would end up horizontal by the time the picture was snapped.

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Hondero Senior Member Offline Posts: 463 Madrid-SPAIN Gender:	Re: Some conclusions from a picture Reply #5 - Apr 23^rd, 2006 at 3:34am Good experience and calculations, Jurek!! In fact I think it´s the easiest way to calculate speeds and spin. On my opinnion your spin there was about 90 degrees for 1/320 s. so it will be 4.800 rpm, like the motor of a car!!
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slingbadger Interfector Viris Spurii Offline Don't Badger a Badger Posts: 3220 Akron NY Gender:	Re: Some conclusions from a picture Reply #6 - Apr 23^rd, 2006 at 11:41am Considering it only takes 8-18 ft.lbs of force to penetrate the face and side of the skull, I would say that getting hit in the heasd with that thing would hurt! Takes 70ft.lbs of force to break the femur, by the way.
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Pikoro

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Re: Some conclusions from a picture
Reply #7 - Apr 23^rd, 2006 at 1:23pm

Fascinating! Shocked

It opens new possibilities as to measuring slinging performance. As long as you have a good camera and are lucky enough to snap the shot at the right moment. Roll Eyes

Yurek, I was wondering. Does your style naturally produce that sort of spin on the projectile? Is this type of spin the same as the Magnus effect? I use a style some what similar to yours, helicopter with sidearm release, so I was wondering if that style produces that sort of spin or you have to do something extra.

I don't know much about slings and the magus effect, so I'm still trying to figure it out.

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mgreenfield Funditor Offline Posts: 509 Milwaukee Wisconsin Gender:	Re: Some conclusions from a picture Reply #8 - Apr 23^rd, 2006 at 4:48pm Yurek, ....absolutely super pictures & calculations!!!! We need more of this from anybody/everybody! Also great demo of the "football" spiral pitch. What grip & throwing style were you using??
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CanDo Interfector Viris Spurii Past Moderator Offline Posts: 1652 New England, USA Gender:	Re: Some conclusions from a picture Reply #9 - Apr 23^rd, 2006 at 9:42pm Wow, don't hit your dog with that thing! This is a great technique I'm going to try it out with at 'latl darts soon- and slings of course too, if I can find someone brave enough to stand near me that is.
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Matthias Past Moderator Offline Posts: 1418 Gatineau/Ottawa QC, Canada Gender:	Re: Some conclusions from a picture Reply #10 - Apr 24^th, 2006 at 12:40am Greatest sling-mechanics pictures so far! The spin visualisation is great, and the numbers for both it and speed seem right on. Matthias
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Yurek

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Re: Some conclusions from a picture
Reply #11 - Apr 24^th, 2006 at 5:43pm

I'm really glad, you guys can appreciate the "scientific" value of that picture

My son is proud of it, Smyk too. Also thanks for some nice words.

Johnny,

I'm not a physics major (if I understand it correctly), I just used to like it, so I remember somewhat from schools, despite it was very long time ago

Tint,

It was rather a sideway (or rather diagonal) snap, not an overhead one, and the trajectory was flat (low), thus my hand is in a lower position. Besides, you see a small jiffy after release point. The pouch and retention cord are invisible, you can only see a part of release cord. The release position of the hand (in a similar technique) you can imagine from the below picture. The release is just the "point-first" type, with a wide grip.

The picture is from the topic:

http://www.slinging.org/forum2/yabb/YaBB.cgi?board=1;action=display;num=11272197...

I'm sure you Mike will be able to find answers for you questions, from the picture. Somewhere was a small movie of me slinging into a tire, it could even say more.

Quote:

So I'm not the only one who slings in their pajama bottoms . By the way, what sling style were you using?

Altay, BTW, in this thread, just about panties, I have exceptionally put some information about slinging, so please,forgive me the off-topic. Sorry, but I think, you are wrong in your explanation.

Hondero,

You probably are right, the rotation speed might be somewhat bigger. That kind of balls is pretty good to demonstrate the Mangus Effect and experiments with it, because of their light weight and... maybe... the dimples.

Pikoro,

The style, for me, usually produces the spiral spin of elongated stones. I have been thinking, that for balls it is unlike, but the picture says something different. Looks like we can sling balls in the "point-first spiral" way. They can go pretty straight.

The strong backspin gives a nice straight trajectory too, when a ball is fast, but in the second half of the fly, the spin can bend the trajectory to the up.

slingbadger, CanDo,

I believe that kind of balls could really hurt in short ranges. They are soft and light, then losing the velocity quickly. Smyk, usually waits for them 50 - 80 m away.

Matthias,

I knew you would like the picture Cheesy

Greetings,

Jurek

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« Last Edit: Apr 25^th, 2006 at 4:53pm by Yurek »

In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.

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