When an object is thrown in air at an angle different from the horizontal, it travels in a curved path, reaches a maximum height, and then then again falls down in a curved path. This path of the projectile is described by a parabola.
Projectile motion vectors:
The velocity of an object during projectile motion can be resolved into two components, the horizontal velocity and the vertical velocity. Since velocity is a vector quantity, these components are called as the horizontal vector component and the vertical vector component of the velocity of the object. The horizontal vector component of the velocity makes the body move forward whereas the vertical vector component of the velocity makes the body achieve a certain maximum height and then fall down.
As explained above, the velocity of a projectile at any point during its motion can be resolved into two vectors, the horizontal velocity and the vertical velocity. If the initial velocity of a projectile is `U m/s` , then its horizontal velocity is given by `U cos theta` and vertical velocity is given by `U sin theta` .
These components of the velocity are also called its rectangular components.
The following diagram represents the resolution of velocity of a projectile into its rectangular components.
The horizontal velocity component of the projectile does not change during the complete motion of the vector, since there is no force acting on it to give it acceleration.
On the other hand, the vertical velocity component of the projectile changes during its motion due to the acceleration given to it by the force of gravity:it decreases as the body moves upwards and becomes zero at the maximum height of the body, and as the object starts falling down its vertical velocity goes on increasing - under the influence of gravity.