There is an apple of 2n weight. By gravity and air resistance, we can calculate the resultant force F1 and F2 when it rises and falls in the process of throwing upward Why F1 = G + F resistance? F2 = G-F resistance?

There is an apple of 2n weight. By gravity and air resistance, we can calculate the resultant force F1 and F2 when it rises and falls in the process of throwing upward Why F1 = G + F resistance? F2 = G-F resistance?

When rising, the resultant force is larger
The direction of resistance is opposite to the direction of motion
When the apple rises, it is subjected to the vertical downward gravity and the vertical downward resistance, and the resultant force is the sum of the two forces; when it falls, it is subjected to the vertical downward gravity and the vertical upward resistance, and the resultant force is the difference of the two forces