Inertia and types of Inertia

Inertia and types of Inertia

What is Inertia :

The resistance to change of state of an object due to its own mass is usually known as inertia. The amount of resistance given by an object to the change of its state is directly proportional to its own mass.

Types of Inertia:

  • Mass moment of inertia
  • Area moment of inertia
  • Polar moment of inertia

Mass moment of inertia:

The resistance of an object to rotate due to its own mass is known as Mass moment of inertia. This inertia is considered when the object is rotating while designing, example : flywheel, governor, impeller, ceiling fan etc. For rotating objects, the Mass moment of inertia i.e resistance to angular velocity or angular acceleration  should be less in order to reduce the power consumption. Here the inertia is taken about the axis of rotation.

Area moment of inertia:

The resistance of an object to bend or deflect is known as Area moment of inertia. But here, this inertia is independent to the mass, the resistance of an object also depends on its area. Imagine, you can bend objects with small area easily, but greater one you may not bend easily, here the inertia is calculated without considering the mass. This inertia is considered when the object is prone to bending or deflection while designing, example : Beams. For beams, the Area moment of inertia should be more in order to resist the bending. Here the inertia is taken about x-x axis, and y-y axis.

Polar moment of inertia:

The resistance of an object to the torsion i.e twist is known as Polar moment of inertia. Twist is different from rotation, hence this type of inertia is different from mass moment of inertia. This type of inertia is considered when the object is prone to twist while applying the torque i.e rotating force. Example : shaft, the polar moment of inertia of the shaft should be more to resist the twist while rotating for efficient power transmission.



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