The benefit of a curved rod is that the curtain can be pulled around the corners of the tub which prevents water from escaping onto the floor. However, a straight rod is easier to install and may be the only option for some stalls and tub spaces.
yes
one is curved one is straight
A two-dimensional shape with one curved side and four straight sides can be created, but there is not specific name for such a shape.
Yes
If you are referring to a shape, then a semi-circle would be the most likely shape that contains one straight side and one curved. Take a look at a protractor, it's a semi-circle.
sphere
A straight or curved line truncated at one point.
target has an adjustable one that goes from like 45" to 75"
Two straight parallel lines. One straight, and one curved is often used to denote a polarized capacitor.
A tangent
It could be a cylinder
A curved stick is more accurate, because the puck rolls off the stick easier.