Balistics
Consider a cannonball fired from a cannon. The barrel of the cannon points at an angle θ from the horizontal. This is known as its elevation. When the cannon is fired the explosion and expansion of the gases created accelerate the cannonball until it leaves the barrel. The velocity with which it leaves the barrel is known as the muzzle velocity.
To understand the motion of the ball, the velocity can be resolved into horizontal and vertical components. Experiments, taking multiple images with strobe light of projectiles, show that the horizontal component of velocity is constant with time. That is, the object travels at the same horizontal speed throughout the motion.
The vertical component has gravity acting against the projectile so its motion is that of an object that has been thrown into the air or dropped from a platform.
When these two motions are combined, the resulting path is known as a parabola.
Even for extended complicated objects the motion is roughly parabolic. Divers diving into a swimming pool, motorcross riders. Although the motion of the object may be very complicated if you work out where the centre of mass is and follow this point, it will move in a parabolic trajectory.
Projectile motion problems can be solved using the equations of linear motion.
Often question about projectiles will ask you to find the maximum height, or the range of the projectile, or even how long it took for the projectile to hit the ground.