Why, in the absence of noticeable external efforts, the size and shape of the solid bodies around us do not change?

Because in the absence of deforming forces, the molecules of the substance are at such distances at which the forces of mutual repulsion are compensated by the forces of mutual attraction.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.