Bullets fired horizontally do eventually fall down due to Earth's gravity. However, the reason they can travel a significant distance before hitting the ground is related to the combination of their initial velocity and the downward acceleration due to gravity.
When a bullet is fired horizontally from a gun, it typically has an initial velocity that gives it a forward momentum. As the bullet moves forward, it is also influenced by the force of gravity acting downward. The key to understanding why it doesn't fall immediately is that the bullet's horizontal velocity remains nearly constant due to its inertia, while gravity acts only vertically, causing it to accelerate downward.
In the absence of air resistance, the bullet will continue to move horizontally with the same speed it had when it left the gun. As it travels forward, the downward force of gravity causes the bullet's path to curve downward gradually, creating a trajectory that resembles a projectile motion.
The time it takes for the bullet to hit the ground will depend on factors such as its initial velocity, the height of the gun above the ground, and the gravitational acceleration. With sufficient initial velocity, the bullet can travel significant distances horizontally before it finally falls to the ground due to the cumulative effect of the downward acceleration from gravity.
It's worth noting that in real-world scenarios, air resistance plays a role in slowing down the bullet and altering its trajectory. The distance a bullet can travel before hitting the ground will be influenced by various factors, including air resistance, bullet shape, initial velocity, and angle of fire.