# Testing projectile motion with a drawn parabola

##### 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

**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=½at^{2}*) 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.*