The most fundamental difference between the 2D and 3D forms is that the 2D is flat and has only 2 dimensions while 3D design allows for depth and rotation.
The difference in detail is discussed below:
2D design involves purposeful decision-making about using the elements and principles of drawing in an integrative manner. In 2-D design, understanding of design principles is demonstrated as applied to a two-dimensional surface. These designs articulate the principles of design, such as unity/variety, balance, emphasis, contrast, rhythm, repetition, proportion/scale and figure/ground relationship, through a range of visual elements, including line, shape, color, value, texture and space.
Example of 2D Design includes posters, logos, brochure, banners etc.
3D design addresses engagement with physical space and materials. In 3-D design, the designer demonstrates understanding of design principles that relate to depth and space and articulates the same principles of design utilized in 2-D design (unity, balance, etc.) with visual elements such as mass, volume, color/light, form, plane, line and texture. These issues are explored through additive, subtractive and/or fabrication processes.
Examples of 3-D design approaches include, but are not limited to, figurative or non-figurative sculpture, architectural models, metal work, ceramics, 3-D fiber arts/fashion and jewelry or other forms of body adornment.
The 2d and 3d form of an alarm clock is drawn below:
