Curve

Another effect of english is what is known as "Curve" or "Swerve". When a cue ball is hit low with a downward stroke using english, the cue ball tends to curve instead of moving in a straight line. This is a similar effect, though to a much lesser degree, to the masse shot. The illustration below shows you what I mean. Notice that the cue stick is at a downward angle hitting the cue ball low. If you put english on this type of shot, an effect called "curve" will be the result.

The direction of the curve will be the same as the direction of the spin. That means that if you have a low right english on the cue ball, it will curve to the left and back to the right. If you have a low left english on the cue ball, it will curve to the right and then back to the left. See the illustration below; the red line indicates a curve generated when low right english is applied with a downward cue stick and the blue line indicates a curve generated when a low left english is applied with a downward cue stick.

The amount curve generated is generally dependent the following:

1. The distance between the cue ball and the object ball. At longer distances, more curve is generated.
2. The amount of spin on the cue ball. The more spin on the cue ball, the more "curve" is generated on the object ball.
3. The speed of the stroke. A softer stroke generally results in more "curve" effect than a harder stroke.
4. The downward angle of the cue stick. The more angle on the cue stick, the more curve is generated.
5. The type of cloth also plays a role here. Again, more friction means the cloth has more "hold" on the cue ball thus the effects of curve is more.

All these factors come into play at the same time so you should adjust your shot with consideration for all the above factors.

Now with all these effects: Deflection, Throw, and Curve... you will need to consider all these things when using english. Only with enough practice will you be able to learn instinctively how the cue ball will react to all these effects.