Direct Measurement Videos > Video Library > Hoop falling from string

Circular shapes falling from string (disk, hoop, bicycle wheel)


Pick a Video:
A solid disk, a hoop, and a bicycle wheel are each suspended from a vertical string and allowed to fall to the floor, unwrapping the string as they go. Students can measure the distance and time as the objects fall.


Instructor Note

When teaching with this video, direct students to the student video library, which provides student access to all videos without links to instructor materials and solutions.
Three videos are each available in two formats for frame-by-frame viewing:

Falling disk:

Falling hoop: Falling bicycle wheel:

Teaching Materials


  • rotational kinematics
  • Newton's Second Law for rotation
  • torque
  • rotational inertia

Sample question:

  • What is the predicted acceleration for the disk and hoop as they fall? Do the disk and hoop in the videos match?
  • Determine the rotational inertia of the bicycle wheel
Note: there is also a prototype version of this, which allows students to position and calibrate measurement tools.