Newton 3rd law forces, what your link refers to as "partner forces", are equal and opposite forces that act on different objects. The motion of an object is due to the net force acting on that object, per Newton's 2nd law. It is sometimes difficult to distinguish these forces without the aid of free body diagrams.

FIG 1 below shows the forces acting on the box, table and Earth for the "stationary" system. The Newton 3rd law pairs are circled in blue. The forces responsible for the motion of the box and table are circled in red.

Note that the normal reaction force of the table acting up on the box is simply the force of gravity acting down on the box. The net force acting up on the block is the normal reaction force of the table minus the downward force of gravity of the box, for a net force of zero. The same applies to the table except that the force acting down on the table is the sum of the gravitational forces acting downward on the box and table.

FIG 2 shows the rocket with the table and box as its only contents. I didn't actually view the link, but when its says "the force of gravity is not a partner force to the force moving upward" what it probable means is the upward force on the box is no longer simply the force of gravity acting down on the box as in FIG 1. As shown in FIG 2 the upward reaction force of the table acting on the box minus the force of gravity acting downward on the box must equal the net upward force on the box responsible for its acceleration.

Hope this helps.

Newton 3rd law forces, what your link refers to as "partner forces", are equal and opposite forces that act on different objects. The motion of an object is due to the net force acting on that object, per Newton's 2nd law. It is sometimes difficult to distinguish these forces without the aid of free body diagrams.

FIG 1 below shows the forces acting on the box, table and Earth for the "stationary" system. The Newton 3rd law pairs are circled in blue. The forces responsible for the motion of the box and table are circled in red.

Note that the normal reaction force of the table acting up on the box is simply the force of gravity acting down on the box. The net force acting up on the block is the normal reaction force of the table minus the downward force of gravity of the box, for a net force of zero. The same applies to the table except that the force acting down on the table is the sum of the gravitational forces acting downward on the box and table.

FIG 2 shows the rocket with the table and box as its only contents. I didn't actually view the link, but when its says "the force of gravity is not a partner force to the force moving upward" what it probable means is the upward force on the box is no longer simply the force of gravity acting down on the box as in FIG 1. As shown in FIG 2 the upward reaction force of the table acting on the box minus the force of gravity acting downward on the box must equal the net upward force on the box responsible for its acceleration.

Hope this helps.

Newton 3rd law forces, what your link refers to as "partner forces", are equal and opposite forces that act on different objects. The motion of an object is due to the net force acting on that object, per Newton's 2nd law. It is sometimes difficult to distinguish these forces without the aid of free body diagrams.

FIG 1 below shows the forces acting on the box, table and Earth for the "stationary" system. The Newton 3rd law pairs are circled in blue. The forces responsible for the motion of the box and table are circled in red.

Note that the normal reaction force of the table acting up on the box is simply the force of gravity acting down on the box. The net force acting up on the block is the normal reaction force of the table minus the downward force of gravity of the box, for a net force of zero. The same applies to the table except that the force acting down on the table is the sum of the gravitational forces acting downward on the box and table.

FIG 2 shows the rocket with the table and box as its only contents. I didn't actually view the link, but when its says "the force of gravity is not a partner force to the force moving upward" what it probable means is the upward force on the box is no longer simply the force of gravity acting down on the box as in FIG 1. As shown in FIG 2 the upward reaction force of the table acting on the box minus the force of gravity acting downward on the box must equal the net upward force on the box responsible for its acceleration.

Hope this helps.

Newton 3rd law forces, what your link refers to as "partner forces", are equal and opposite forces that act on different objects. The motion of an object is due to the net force acting on that object, per Newton's 2nd law. It is sometimes difficult to distinguish these forces without the aid of free body diagrams.

FIG 1 below shows the forces acting on the box, table and Earth for the "stationary" system. The Newton 3rd law pairs are circled in blue. The forces responsible for the motion of the box and table are circled in red.

Note that the normal reaction force of the table acting up on the box is simply the force of gravity acting down on the box. The net force acting up on the block is the normal reaction force of the table minus the downward force of gravity of the box, for a net force of zero. The same applies to the table except that the force acting down on the table is the sum of the gravitational forces acting downward on the box and table.

FIG 2 shows the rocket with the table and box as its only contents. I didn't actually view the link, but when its says "the force of gravity is not a partner force to the force moving upward" what it probable means is the upward force on the box is no longer simply the force of gravity acting down on the box as in FIG 1. As shown in FIG 2 the upward reaction force of the table acting on the box minus the force of gravity acting downward on the box must equal the net upward force on the box responsible for its acceleration.

Hope this helps.