Try flicking an eraser off the edge of a table at the same time as dropping one. You should notice that they reach the ground at the same time. This demonstrates the independence of vertical and horizontal motion for a projectile.
Key Concepts
A projectile is any body in motion, on which the only force acting is weight. The free-body diagram is identical to that on the Acceleration due to gravity page.
This means that:
- vertically, the object has constant acceleration and so suvat equations can be used
- horizontally, the object has zero acceleration and so we can return to an old friend \(\text {speed} = {\text {distance} \over t}\)
We must assume that no horizontal forces (e.g. drag) act at any time. This means that the body is modelled as a particle.
We can think of projectile motion as two problems in one: constant velocity horizontally and constant acceleration vertically. The motions in both directions have one common feature... time!
How much of Projectile motion have you understood?