For any projectile launched at an angle, the projectile will have an initial horizontal velocity as well as an initial vertical velocity.
For, example, let's say that you launch the same cannonball we use in this lesson at an angle this time.
Once the cannonbal is in the air, let us see how this will affect the vertical speed and the horizontal speed.
First, let us talk about the horizontal speed.
Good news! Whether the projectile is launched horizontally or at an angle, there is still no horizontal force acting on the cannonball . And again with no horizontal force, there is no horizontal acceleration. And with no horizontal acceleration, the cannonball will once gain move horizontally with constant velocity.
Now, what about the vertical speed? When an object is thrown straight up into the air, little by little the speed will decrease until the speed is zero. Gravity will keep decreasing the speed. Then, the object will go down with increasing speed. Gravity will keep increasing the speed.
Let us put together the vertical and horizontal movement/speed of the cannonball to see what we will get. See below the horizontal speed, the vertical speed, and the resultant speed in brown. Once again, you can see that the ball move along the orange curve which is a parabola. The vectors shown in brown are tangent to the orange curve or parabola.