A cannon recoils when fired due to Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction. Here's a breakdown:

* Action: The cannon expels the cannonball with a high velocity and force.

* Reaction: The cannon experiences an equal and opposite force, pushing it backward. This is the recoil.

Here's how it works in detail:

1. Momentum Conservation: The total momentum of the system (cannon + cannonball) before firing is zero.

2. Firing: When the cannon fires, the cannonball gains momentum in one direction. To conserve momentum, the cannon must gain an equal amount of momentum in the opposite direction.

3. Recoil: The cannon's momentum is manifested as a backward movement, which is the recoil.

Factors affecting recoil:

* Mass of the cannonball: A heavier cannonball will cause a stronger recoil.

* Mass of the cannon: A heavier cannon will experience less recoil for the same cannonball.

* Velocity of the cannonball: A higher velocity cannonball results in a stronger recoil.

* Angle of firing: Recoil is greatest when firing horizontally.

Practical implications:

* Cannon design: Cannons are designed to absorb recoil through various mechanisms like recoil springs, hydraulic brakes, or the use of heavy carriages.

* Safety: Understanding recoil is crucial for safe operation of cannons and other firearms.

* Weapon effectiveness: Recoil can affect accuracy and rate of fire, particularly in lightweight weapons.

In essence, the recoil is a natural consequence of the conservation of momentum, and it demonstrates the fundamental principle of action and reaction in physics.