plane diagram in a sentence

1. The small graph above each pendulum is the corresponding phase plane diagram; the horizontal axis is displacement and the vertical axis is velocity.
2. To formulate the Euler Cauchy stress principle, consider an imaginary surface S passing through an internal material point P dividing the continuous body into two segments, as seen in Figure 2.1a or 2.1b ( one may use either the cutting plane diagram or the diagram with the arbitrary volume inside the continuum enclosed by the surface S ).
3. It's difficult to find plane diagram in a sentence.