Physics Lab Equipment

LEMI-18 Rotational Moment of Inertia Apparatus

LEMI-18 Rotational Moment of Inertia Apparatus


  • Optical rail for simple adjustments

  • High accuracy

  • Affordable


Moment of inertia is a physical quantity for the representation of the inertial amount of a rotational object. It is dependent on the mass distribution and the shaft position of the rigid body.


This apparatus uses the three-string pendulum method to determine the moment of inertia of a rigid body. A photoelectric sensor combined with a time counting device is used to measure the torsional oscillation period of a hanging plate. Through the experiments, students can understand the physical principle of the moment of inertia and learn the measurement method with factors related to the amount of moment of inertia.


Using this apparatus, the following experiments can be conducted:


1. Measure the moment of inertia using the three-string pendulum method

2. Measure the moment of inertia of two objects of same mass but with different mass distribution

3. Verify the parallel axis theorem of moment of inertia

The instruction manual contains experimental configurations, principles, step-by-step instructions, and examples of experiment results. Please click Experiment Theory and Contents to find more information about this apparatus.


String Length of the Pendulum> 500 mm
Timing Resolution1 ms
Preset Count Number< 66
Specimensmall cylinder (2), circular disc (1), circular ring (1)

Part List

Main Unitincl base, slider, hanging arm, hanging disc, starting disc, pendulum strings
Laser Diode1
Counting Timer1
Connection Wire2
Circular Lever1
Cylindrical Sample2
Disc Sample1
Ring Sample1

LEMI-18 Rotational Moment of Inertia Apparatus.png

Schematic of system

(Click figure to enlarge)

 LEMI-18 Rotational Moment of Inertia Apparatus.png

Three-string torsional pendulum

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