A book rests on a table. Identify the NIII force pairs.
The Attempt at a Solution
Downward force of book on table; upward force of table on book (N).
Downward force of book and table on ground; upward force of ground on book and table (N).
Downward force of earth on book, table and ground (gravity); upward force of book, table and ground on earth.
This is where I get confused. The earth and the ground are essentially the same thing, aren't they?
Also, the book is in equilibrium because the normal force of the table and gravity cancel.
The table is in equilibrium because the normal force of the ground and gravity cancel. So why is the ground in equilibrium? Are all normal forces essentially directed from the center of the earth, as is gravity?