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).