Comment on whether the following pairs of forces are examples of action-reaction: (a) The Earth attracts the Earth. (b) A propellered airplane pushes air toward the tail; the air pushes the plane forward. (c) A horse pulls forward on a cart, moving it; the cart pulls backward on the horse. (d) A horse pulls forward on a car without moving it; the cart without moving it; the Earth exerts an equal and opposite force on the cart. (f) the Earth pulls down on the cart; the ground pushes up on the cart with an equal and opposite force.

In accordance to Newton’s third law, when one body exerts a force on another, the second exerts a force on the first. These two forces are always equal in magnitude and opposite in direction.
(a) The Earth exerts a gravitational force on the brick, and the brick exerts a same amount of force on the earth. Therefore the pair of forces is the example of action and reaction.
(b) A propellered airplane pushes air toward the tail. At the same time in accordance to Newton’s third law the air pushes the plane in the forward direction with same amount of force. Therefore the pair of forces is the example of action and reaction.
(c) A horse pulls forward on a cart, moving it. At the same time in accordance to Newton’s third law the cart pulls backward on the horse. Therefore the pair of forces is the example of action and reaction.
(d) A horse pulls forward on a cart without moving it. At the same time in accordance to Newton’s third law the cart pulls back on the horse. Therefore the pair of forces is the example of action and reaction.
(e) A horse pulls forward on a cart without moving it. At the same time in accordance to Newton’s third law the cart pulls backward on the horse. But the Earth exerts an equal and opposite force on the car is the frictional force. Due to this the cart will not move. Therefore the pair of forces is not the example of action and reaction exactly.
(f) The Earth pulls down on the cart. At the same time in accordance to Newton’s third law the ground pushes up on the cart with an equal and opposite force. Therefore the pair of forces is the example of action and reaction.