FORM is three-dimensional (height, width, and depth) and encloses volume For example, a triangle, which is two-dimensional, is a shape, but a pyramid, which is three-dimensional, is a form. Cubes, spheres, pyramids, cones, and cylinders are examples of various forms.
To see a variety of forms click here for a prism, cylinder and sphere click here for more, including a cone
DIFFERENCE BETWEEN SHAPE AND FORM An area of color or an area defined by an enclosed line on a flat surface is a 'shape'. It is two-dimensional, consisting only of height and width, but not of depth.
The three-dimensional mass or volume is called a 'form'. It consists of height, width and depth. The cube above appears to have depth although it is on a flat surface - it is an illusion of a form. A cardboard box, a ball, a pyramid in the desert - these are all examples of a three-dimensional form. You can see a form from many angles, whereas a shape is visible only from a certain number of angles.
HOW TO SHOW FORM Shading of Lights and Darks When drawing or painting, one way to show the three-dimensionality of the subject is to shade the light and dark areas, also known as tones, or values. When working in black-and-white or color, subjects have varying values of light and dark, on a scale from white to black, or grayscale.
Geometric objects, like a cube, will have more sharply defined areas of differing tones, depending on the amount and types of light in a room. These will have a smaller number of tones represented, and these will have sharper edges of tones. EXAMPLES
To depict a cube, only three tonal values are necessary: the side which receives the most light being the lightest, the side furthest from the light source (the darkest), and a middle grey tone for the side which receives an in- between or indirect amount of light.
Natural objects, on the other hand, can have an endless number of tones represented, and these will often have softer, less defined edges.