Drift

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Spin Lizard said:
Your refusal to accept the magnus effect as the cause of drift is somewhat amusing Dave. What is your alternative?
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I'm not refusing to believe it, I've just not seen an explanation or a visual breakdown of what happens that I can comprehend in relation to the Magnus effect. I know what happens, there's all the evidence in the world and all of your explanations, that say it happens, I even get it to happen on the rare occasion, but a part of me wants to know why it happens and how it happens. I just don't see how the Magnus effect causes the drift in the opposite direction to the spin. All of the basic demo's see the ball heading in the direction of the spin. Top spin - the ball goes down, back-spin the ball tries to go up e.g. stops it from dipping. Side spin with horizontal seam the spin is anti-clockwise and the ball follows to the left and vice versa.:(

All of those movements make total sense. I can see why a seamer's ball swings left and right, that all makes sense, all of the illustrations and explanations with regards to the turbulence and drag are clear and comprehendible.

But Drift??????? I'm absolutely baffled still
 
Just seen this again from earlier on in the thread, this is having some resonance with my way of visualising it... Especially in relation to the video of the top-spinner by Warne in this vid linked that uses a scrambled seam.

If you sit with the ball in your fingers and rotate it at 90 degrees to the wicket (ie if you were to try and get the maximum movement of the pitch) you can imagine the top of the ball moving the air to the left (so imparting a *push* to the right on the ball). Simultaneously the bottom of the ball will be exerting the same amount of force on the air as the top, so countering any drift. This is the case if the ball is moving at a constant height.
However if you think that as the ball starts dropping then the air on the left hand side is exerting more force on the left side of the ball than the right. In my mind this is kind of like the airfoil effect on airplanes. This also matches what we all seem to notice - when the ball drops you get a more movement to the right. When the ball is going upwards you see the opposite effect - the ball drifting to the *left*. I do see this effect when I've given it a big rip and can see a perfect colour presented when using a red/white ball - upwards slight left movement, downwards right movement.
 
someblokecalleddave said:
I just don't see how the Magnus effect causes the drift in the opposite direction to the spin. All of the basic demo's see the ball heading in the direction of the spin. Top spin - the ball goes down, back-spin the ball tries to go up e.g. stops it from dipping. Side spin with horizontal seam the spin is anti-clockwise and the ball follows to the left and vice versa.:(
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But there's no reverse magnus effect going on - it's going in the right direction!
 
Yay!!!! I think I've got it at last, just working on the links and a diagram now... Watch this space...

Have a look at this vid and just confirm that the last arrow that he introduces to the image is the direction the ball is going to veer towards.

 
Right here we go, I hope this makes sense. Last night I couldn't sleep thinking about this and I kept trying to visualise why this might happen. I had some of the things Pencil cricket had written about going on in my head and some of the stuff in the Woolmer analysis. But last night the thing I was mulling over was the fact that the drift happens at the end of the flight. Somewhere along the way in all of the explanations someone had said that the fact that the ball was dropping was a key part of the equation. This morning my older son who's much better than me at maths was explaining his theory and some of what he was saying had a ring of truth and an obvious connection with the Magnus force. Again using a ball I tried to visualise what might happen and why. Then the eureka moment happened... I realised I was only thinking about the ball travelling along one plane and obsessing about the forward motion only in relation to the Magnus force. Others had said the drop was a factor and as soon as I started to think about the drop in relation to the Magnus force it started to come together and make sense, but I was still sceptical and unsure how it would be visualised as a diagram.

Then I read the old post by the bloke earlier in this thread realising I'd never read it before, but as I read it, it made sense with regards to my visualisations earlier in the day. I then found the video above and realised that this like most of the others, this relates to balls either dipping (top-spin) or balls that hold up in the air or in the case of base ball side-ways swerve. I then thought - it's the drop! The drop is the factor - the ball going through the air initially is much faster than the drop stage and will also be running out of spin, it's something about the drop - the Magnus force comes into action as the ball starts to drop. I then thought of the same diagrams that have so far completely confounded me and visualised them on their sides. As soon as you do that it makes total sense...

The dropping ball then goes through a different plane and meets the same physics as the ball moving horizontally through the sky, but as you've all pointed out and explained in different ways, the reaction of the ball is the opposite to the spin and this exactly fits the theory offered by the Magnus force...
Drift%2B-%2Bmagnus%2Bforce.jpg
 
It's not quite the whole picture Dave but you are getting there! Perhaps that visualisation shows that it makes sense that it can drift to leg. It is crucial to see that the magnus effect is defined by the direction of ball travel, which I think you are getting.

The reason it's a bit more subtle than your picture is because if you just dropped a spinning ball onto the ground, it ain't going to drift because it just hasn't got the speed. The cricket ball won't be dropping very fast. You can't quite just look at the vertical component in isolation. You have to consider the exact direction of the ball travel.

But you can see that a horizontal ball can drift to leg with a range of spin axes, and also a vertical ball can drift to leg, again with a range of spin axes. Now, what is going on is that a ball which is travelling both forward and down can also drift to leg with a range of spin axes, and the pure leg break is part of that range.

I hope I'm being helpful
 
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gets back to that 5 ball diagram where they've 'flattened' or normalised the flight path arrows so the angle of the ball changes instead.

there is a small amount in the direction of spin on the way up, an equivalent away from the spin on the corresponding downward, and a larger amount as the ball gets steeper downward.

And as Cleanprophet says, environmental factors come into play as to how much of the drift being generated is realised as movement through the air. I describe the day as 'heavy air' where it goes the best. Also the best day to throw a frisbee.
 
boogiespinner said:
It's not quite the whole picture Dave but you are getting there! Perhaps that visualisation shows that it makes sense that it can drift to leg. It is crucial to see that the magnus effect is defined by the direction of ball travel, which I think you are getting.

The reason it's a bit more subtle than your picture is because if you just dropped a spinning ball onto the ground, it ain't going to drift because it just hasn't got the speed. The cricket ball won't be dropping very fast. You can't quite just look at the vertical component in isolation. You have to consider the exact direction of the ball travel.

But you can see that a horizontal ball can drift to leg with a range of spin axes, and also a vertical ball can drift to leg, again with a range of spin axes. Now, what is going on is that a ball which is travelling both forward and down can also drift to leg with a range of spin axes, and the pure leg break is part of that range.

I hope I'm being helpful
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Yeah I get that, hence the fact that the ball dips as well, to illustrate the forward moving component and the dropping component would be quite tricky, I may have a go at doing it, but for the moment I'm quite happy that I've arrived here. I just could not see why the ball would veer towards leg and now I've got something that explains it. Basically it seems that resistant forces exert themselves on the ball as it moves through the air, but you have to imagine those forces on differing planes - horizontal, diagonal (dipping) and steep diagonal (nearing the ball hitting the ground). Each stage has a differing impact on the ball, because both the speed and the revolutions are fading, but the presentation of the balls surface and spinning rotation is maintained as it moves along its trajectory. But that maintained surface/spin/trajectory then is affected by their relationship as they change going through the resistance offered by the air.

If I had some kind of 3D modelling software I'd illustrate it going from a horizontal plane through to a more diagonal plane towards a vertical plane. With regards to Spin Lizards added complexities, I'm not going to go into that, but know where he's coming from and there's all that stuff about balls swinging at Trent Bridge and then not swinging as much once they'd built some new stands.
 
someblokecalleddave said:
there's all that stuff about balls swinging at Trent Bridge and then not swinging as much once they'd built some new stands.
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So much is mentioned about various esoteric factors, humidity, pressure, magnus effect etc but I have one factor which I suspect gets overlooked. Maybe I'll write an academic paper about it.

A wind can simply blow the ball sideways!
 
Spin Lizard said:
gets back to that 5 ball diagram where they've 'flattened' or normalised the flight path arrows so the angle of the ball changes instead.

there is a small amount in the direction of spin on the way up, an equivalent away from the spin on the corresponding downward, and a larger amount as the ball gets steeper downward.

And as Cleanprophet says, environmental factors come into play as to how much of the drift being generated is realised as movement through the air. I describe the day as 'heavy air' where it goes the best. Also the best day to throw a frisbee.
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I'm glad you used the old ' ' around heavy air because it may feel like that but it definitely isn't:

http://www.theweatherprediction.com/habyhints/260/
 
hahaha no science behind it, its just how I've always thought of it. Warm, little to no breeze, cigarettes tend to go down really nicely. Heavy air.

Alright, I'll read the article and get some education. Cheers for the link. :)
 


Dave for you I have designed the above MAGNUS FORCE KEY. Imagine it is a three-dimensional key.

To use:

1) Align the key in the direction of ball travel.
2) Rotate the key so that it covers the spin axis of the ball. (based on Right-Handed corkscrew)
3) The arrow now points in the direction of the magnus force!
 
boogiespinner said:


Dave for you I have designed the above MAGNUS FORCE KEY. Imagine it is a three-dimensional key.

To use:

1) Align the key in the direction of ball travel.
2) Rotate the key so that it covers the spin axis of the ball. (based on Right-Handed corkscrew)
3) The arrow now points in the direction of the magnus force!
Click to expand...
Oh blimey, I've saved it as a file, I'll open it Photoshop now and enlarge it so that I can see it properly, I'm crapping myself in case it undoes the 'Apparent' clarity I have on the subject at the minute, my clarity might be fleeting and temporary:(.

Boogiespinner, sorry mate I'm not getting it, it makes feel like I'm completely thick, as I'm sure other people would look at it and think 'Ah, that's a really good way of illustrating/explaining drift'. I'm looking at it and thinking I need to know some really basic things like where would the pitch be in relation to this?
 
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Oh man! I've done it the wrong way around. It has the wrong handed-ness. The spin axis bit should be on top. I got my corkscrew muddled with a leg break.

So please do ignore that picture.

(the pitch has nothing to with the magnus force though)
 
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