Mass and form

In the first picture we can see how simply shading in a different way can add to the perceived mass of an object. Our eyes don't always need complex shading to be able to recognise an object, and so if shading and detail isn't needed, it may be best to do something like I have with the first onion, and how it uses simple lines to show the form and shape, such as the convex curves. Whereas the second onion and the orange are more focussed on the shading to give a sense of mass and how a particular object reflects light, determined by the texture of it. Shading is also the way we show the internal structure of an object (i.e. everything inside the outline) that wouldn't be clear otherwise which can be seen in the second onion where some parts are raised and some lower.

The second image is a simple arrangement of some items I had lying around; sellotape, a glass and a desktop microphone. I made this arrangement in this simple line drawn style to show that you don't need to shade to be able to create depth in a drawing. These objects were also deliberately chosen because they contain many concave and convex curves which can create interesting shapes. It can be useful to do drawings like this because it helps us break down objects into simple shapes which is good for 3D modelling.