Projectile questions involves particles moving through the air subject only to the force of gravity.

The path of a projectile is illustrated below.

The following points should be noted.

The acceleration is alwaysThe negative sign means the acceleration is directed downwards.

At the maximum height, the vertically velocityis zero. The particle may still be moving horizontally but is not moving up or down.

The motion of the particle is symmetric, with a vertical line of symmetry through the point of maximum height.

There is no horizontal acceleration so the horizontal velocity is constant:whereis the initial velocity andis the angle the initial velocity makes with the horizontal.

The path of a projectile is a parabola, since the equation describing projectile motion can be expressed as a quadratic.

Projectile motion usually assumes no air resistance, which implies the symmetry in (3).