A Topspun Ball Moving Through the Air
In the above diagram, the wind is in quotes, because it is created by the direction the ball is traveling. It's the same as riding a bike on a still day. It will feel as though there is a breeze in your face. The arrows on the ball indicate the direction the ball is rotating. When the arrows point in the same direction as the 'wind direction' a slight vacuum will form.
Nature doesn't like vacuums and will tend to try and fill it. The way this occurs is by surrounding objects filling the void. In this case, it is the table tennis ball. The ball will tend to drop into the vacuum. This explains why top spun shots will drop quickly.
