Can you help me please ? With some details.. thank you ^^
The “reaction” force is a gravitational force acting vertically upwards on the Earth.
The “reaction” must be:
① A force of the same type, i.e. a gravitational force since the action is a gravitational force.
② A force of the same magnitude.
③ A force acting in the opposite direction, i.e. vertically upwards since the action acts vertically downwards.
④ Act on a different object. More specifically it must act on the object that is exerting the “action” force on the apple. I.e. the force must act on the Earth since the action is the gravitational force of the Earth on the apple.