Testing projectile motion with a drawn parabola

Demonstration

This is a demonstration which shows that motion can be predicted.

Health & Safety and Technical notes

Read our standard health & safety guidance

Procedure

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.

Teaching notes

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.

Related experiments

Multiflash photographs of projectiles