# Measure the max angle of a 3D pendulum

• cuallito

#### cuallito

Hi, I need a simple way to measure the maximum angle/vertical displacement of a 3D pendulum (weight hanging from a rope) undergoing random impacts. What will work?

Whelp, you could buy a \$50,000 3-D camera measurement system and software, or you could use your hand and a tape measure. What's your pleasure?

Let the rope pass through a hole in a table. Place a radial array of flat rulers on the table. They will be pushed away by the pendulum rope. Read the distance they are pushed, with y = height of fulcrum above the table, and x = maximum push of ruler, theta = Atan( x / y ).

See; https://en.wikipedia.org/wiki/Ballistic_pendulum

You could use a common video camera. It won't be as accurate as a true high speed camera, but it should suffice for experimental purposes. Mount the camera in front of the pendulum at the height of the pendulum at rest. Put a screen behind the pendulum with a pattern of squares on it. Place the screen the same distance from the pendulum as the camera (makes calculating height and swing easier). Even better, two cameras and two screens at 90 deg. from each other.