Testing projectile motion with a drawn parabola
This is a demonstration which shows that motion can be predicted.
Apparatus and materials
Health & Safety and Technical notes
a Draw a rough parabola by sketching vertical and horizontal lines on a blackboard or whiteboard (see diagram).
b Throw a small object in a vertical plane parallel to the blackboard and near it, so that it follows the curve. With the proper start, the object follows surprisingly well. It is better to start with a parabola which results from throwing the object horizontally.
1 After trying horizontal projection, you could be more adventurous and try the more elaborate path of a complete parabola (see below). Give the object an initial velocity which has both horizontal and vertical components.
2 Discuss how you managed to draw such a perfect parabola, using the idea that the resulting motion for the horizontal (x=vt) and vertical (y=½at2) components of the motion is a parabola.
3 Their velocity at each instant is a tangent to the parabolic path. The components of a velocity add as vectors.
4 A related experiment shows that the horizontal and vertical motions of a projectile are independent of each other: a video of Monkey and Hunter is freely available from the National STEM Centre eLibrary.
This experiment was safety-checked in March 2005.