Each of us has a different way of learning and these are known in Pedagogy as learning styles. My own preference is called Kinaesthetic and works best when I actually try things out and do them - usually again and again and it works best if it's something I have to do all the time. Whereas some people can simply read stuff and make sense of it, that's something I'm not so good at 'Abstract Conceptualisation'. So in the past when I've been reading up on Drift trying to get my head round it and making sense of it in practical terms, I've generally been linked to articles and videos on and about the Magnus effect. Despite reading and watching all these, the penny has never quite dropped, I've never quite got all the explanations and illustrations. But today I've come across an article and an explanation that made it as clear as daylight in a couple of short paragraphs and all because of one really simple explanation that I was able to relate to and understand and it was a written piece. So, here it is in my own words and later the link to the website that finally calrified what Drift is caused by and why............
If you're spin bowler, you'll understand the basic principles simply by empirical observation of your own bowling and probably from tennis and table tennis. Top Spin causes the ball to dip. The usual analogy is that a tennis player slices the ball with the racket across the top of the ball imparting top spin and the ball dips violently over the net. Same with your Top-Spinner in cricket you impart over-spin (Top-Spin) and the ball falls short of the batsman despite being bowled at a speed that would normally mean the ball would end up at his feet or around about his knees. Back Spin on the other hand does the opposite, the ball floats through the air maintaining a relatively straight trajectory - not dipping anywhere as expected. Footballers apparently do this particularly well slicing the ball under-neath so that it stays straight through the air - even rising in some instances till it reaches a point where its speed means it eventually starts to dip.
So....How do they do that? The explanation goes like this. A spinning ball as it spins creates a layer of air immediately around it that spins in the same direction that the ball is spinning. If the ball is also moving forwards e.g. with Top-Spin, the direction of the spinning ball will mean that its layer of air will be moving around the ball with the same direction, so at the top of the ball, the spinning air will be colliding with the air that its moving through, whereas the spinning air at the bottom of the ball will be helped along with air that it's meeting as they're moving in the same direction thus making the ball dip. The backspinning ball does the opposite, the air at the bottom of the ball is rotating against the air its meeting and so lifts the ball and prevents it from dipping.
For me that was it, that explanation worded slightly different here http://www.catcheswinmatches.com/coaching/spin/ suddenly made me realise what was going on and now I know how and what I need to do to get the ball to drift!