Explanation of how a cart pulled by a horse can be moved:

Action and Reaction:
- According to Newton's third law of motion, for every action, there is an equal and opposite reaction. This means that when a force is exerted on an object, the object exerts an equal force in the opposite direction.

Horse pulling the cart:
- When a horse pulls a cart, it exerts a force on the cart in the forward direction. This force is the action.
- As a reaction to this force, the cart exerts an equal and opposite force on the horse. This reaction force is what propels the cart forward.

Friction and Traction:
- The wheels of the cart provide traction against the ground, which allows the cart to move forward.
- The friction between the wheels and the ground also plays a crucial role in moving the cart. As the horse pulls the cart forward, the wheels overcome the frictional force between them and the ground, allowing the cart to move.

Combined forces:
- The combined forces of the horse pulling the cart, the reaction force of the cart on the horse, and the friction between the wheels and the ground work together to move the cart forward.

Conclusion:
- In conclusion, the action of the horse pulling the cart creates a reaction force that, combined with traction and friction, allows the cart to be moved forward. This demonstrates Newton's third law of motion in action.