student
What do you think is hollow inside: a ball or a sphere? by 21:33:46
Dmitry
The Sphere. Monolithic bullet 21:34:12
student
But it is strange that the balloon is hollow 21:34:36
Although, if you think, we call a ball the air that is inside the spherical shell.
But then you can not hold anything in your hands, claiming that you have a balloon in your hands.