Balls
A quadrilateral.
A triangle.
Side by side, they would form a rectangle. From part-side touching part-side through to corner to corner, they would form a shape somewhat like a figure of eight. There are other possibilities - eg corner of one touching the side of the other.
If there are no angles, all you have is a 'straight side'. There is a plane and no shape. Maybe you are thinking that straight means standing up straight. You might then be thinking of an upright tube.
Balls
A quadrilateral.
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.
A triangle.
Side by side, they would form a rectangle. From part-side touching part-side through to corner to corner, they would form a shape somewhat like a figure of eight. There are other possibilities - eg corner of one touching the side of the other.
If there are no angles, all you have is a 'straight side'. There is a plane and no shape. Maybe you are thinking that straight means standing up straight. You might then be thinking of an upright tube.
A shape with at least one side that is not straight, a shape where a pair of straight lines cross one another (like an angular figure of 8).
Extend any straight side of a shape. The angle made by that side with the adjacent side of the shape is an exterior angle. Its value is 180 degrees less the interior angle.
Yes
There is no specific name for such a shape.
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.
A scalene triangle.