The point is a square with a side length 1 yocto (the yocto is the smallest unit of measurement and it is equal to 10^-24 meter)

The line segment: is a group of points that lie in the same line and the angle between each point and the other = zero. Circumference of any shape=number of points ×length of point

The circle: is a flexion of a line segment to shape to make the circular shape, and the angle between each point and the next one is a constant along the circle and greater than zero.

The tangent: is the line segment that has only one common point with the circle, although if it has another common points with a part of the tangent and this definition is consistent with the basic definition.

The power of the gravity affects the motion of the body, makes it curved, and consists a parabola, this is because of the air resistance

the surface of the water in a glass is a plane, and if we considered that there is no wind for the surface of the water to be static, in that case the water will be spherical because of the gravity and the communicating vessels, so how we see the water as a plane and from afar a spherical ?

How to bend the metal: known that when the metal arched it expands to fill the spaces (the triangles), and by putting database with the number of units, and the length of the maximum angle for the metal piece is one meter, and in the form of a cuboid with length and thickness of 1cm.

References: rms.html ircleAngles.htm es/M124_Sec3.2_App_Radian_Measure.pdf homepage.eircom.net/~phabfys/circles.html