Understanding Action and Reaction
The principle of action and reaction, as described by Newton's Third Law of Motion, states that for every action, there is an equal and opposite reaction. This principle plays a crucial role in how a horse can pull a cart.

Force Exerted by the Horse
- When a horse pulls a cart, it exerts a forward force on the harness attached to the cart.
- This force is generated by the horse's muscles as it pushes against the ground with its hooves.

Reaction Force from the Ground
- As the horse pushes backward against the ground, the ground exerts an equal and opposite force forward on the horse.
- This reaction force propels the horse forward, allowing it to pull the cart.

Friction and Movement
- The wheels of the cart also play a significant role. They reduce friction between the cart and the ground, making it easier for the horse to pull the cart.
- If the cart were on a surface with high friction, the horse would need to exert more force to overcome this resistance.

Combined Forces for Motion
- The horse's ability to pull the cart relies on a combination of its strength, the friction from the ground, and the reduced friction from the cart's wheels.
- Thus, as the horse moves forward, it continuously exerts force on the cart while the ground provides the necessary support through the reaction force.

Conclusion
In summary, the horse can effectively pull a cart due to the interplay of action and reaction forces, the mechanics of friction, and the design of the cart's wheels, demonstrating Newton's laws in action.