In projectile motion, the velocity of an object does change as it moves through its trajectory. However, the magnitude of the velocity remains constant if there is no external force acting on the object in the direction perpendicular to its motion.
Projectile motion refers to the motion of an object that is launched into the air and moves along a curved path under the influence of gravity. The key factors influencing the motion are the initial velocity, the launch angle, and the acceleration due to gravity.
While the object is in the air, it experiences a constant downward acceleration due to gravity, which acts vertically downward and doesn't affect the horizontal component of velocity. This means that the horizontal velocity remains constant throughout the motion, as there are no forces acting on the object horizontally.
On the other hand, the vertical velocity changes continuously due to the effect of gravity. As the object moves upward, its vertical velocity decreases until it reaches its highest point where it momentarily becomes zero. Then, as the object descends, the vertical velocity increases in the opposite direction until it reaches the ground.
Although the magnitude of the velocity changes in the vertical direction, the horizontal velocity remains constant because no forces are acting horizontally. This is known as the principle of independence of motion, where the horizontal and vertical components of motion are treated separately.
To summarize, the velocity in projectile motion does change, but the magnitude of the horizontal velocity remains constant as long as there are no external forces acting in that direction. The change in velocity primarily occurs in the vertical direction due to the influence of gravity.