All 4 Uses of

demonstrate
in
The Glass Castle

They'd stick their heads into her classroom and see the students playing tag and throwing erasers while Mom was up front, spinning like a top and letting pieces of chalk fly from her hands to demonstrate centrifugal force.
p. 74.3

demonstrate = show (how something works)

They were filled with the things Mom had inherited from Grandma Smith: a dark Spanish dining table with eight matching chairs, ... and glass-fronted cabinets filled with Grandma's bone china, which Mom demonstrated was the finest quality by holding a plate up to the light and showing us the clear silhouette of her hand through it.
p. 94.5

demonstrated = showed

He told Lori he would help her write a paper that would demonstrate that Shakespeare's plays had multiple authors, like Rembrandt's paintings.
p. 227.5

demonstrate = show

Brian made eggnog; and to demonstrate that he was on his best behavior, Dad went to great lengths to make sure there was no alcohol in it before he accepted a glass.
p. 263.3 *

Definitions:

(1) (demonstrate as in: It demonstrates my point.)
to show
The exact meaning of this sense of demonstrate can depend upon its context. For example:
- "I will demonstrate how to throw a Frisbee." -- show how to do something
- "I will demonstrate how much quicker the new computer is than the old one." -- show how something works
- "Her questioned demonstrated that she was listening and thinking deeply about what was said." -- showed to be true or proved
(2) (demonstrate as in: demonstrate to protest)
a public display supporting a cause -- usually joining with others in a political protest