## Testing projectile motion with a drawn parabola

Practical Activity for 14-16

**Demonstration**

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

Apparatus and Materials

- Object, small

Health & Safety and Technical Notes

Read our standard health & safety guidance

Procedure

- Draw a rough parabola by sketching vertical and horizontal lines on a blackboard or whiteboard (see diagram).
- 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

- 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.
- 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*=½ at^{ 2 }) components of the motion is a parabola. - Their velocity at each instant is a tangent to the parabolic path. The components of a velocity add as vectors.

*This experiment was safety-tested in March 2005.*

- A related experiment (Monkey and Hunter) shows that the horizontal and vertical motions of a projectile are independent of each other: