I discovered a new way to define a circle. Make a cone out of a paper or anything else and observe it's shadow in the sun .First, hold the cone as such it's base is parallel to the ground and the axis of the cone is perpendicular to the ground. The shadow will be a triangle.Then, tilt the top of the cone such that it makes an angle from the vertical and go on increasing it ,you will notice that the apex of your triangle(the previous shadow) will slowly demolish and what you will get is a complete circle. Definition : When a cone is kept in the sun , and it is tilted with an increasing angle from the vertical , it's shadow disintegrates from a triangle into a circle.
I don't know if it is of any use but I just came across it and thought it best to share..Please give your views about this @nihar mahajan,@Calvin lin,@Brian Charlesworth@sharky kesa