# Calculate the moment of inertia of an object

1. Nov 21, 2013

### Panphobia

So we just learned about moment of inertia in my first year physics class, and how to calculate it. Though I do know how to calculate the moment of inertia of an object, I don't really know what it is. I tried looking on wikipedia and the explanations just seem to be equations. What exactly is the moment of inertia in semi layman's terms?

2. Nov 22, 2013

### SteamKing

Staff Emeritus
It's a measure of the resistance of a body to undergo rotational motion due to the application of a torque to that body. It's analogous to the effect that the mass of a body has on the amount of acceleration produced by a given force applied to that body.

For a given body of mass 'm', the application of a certain force F will produce an acceleration 'a'
(F = ma). If the mass is doubled and the force remains the same, the acceleration will be half of the original amount.

For rotation, the moment of inertia J is the constant of proportionality between the applied torque T and the rotational acceleration α, such that T = Jα.

3. Nov 22, 2013

### Panphobia

So basically it is a measure of how easy it is for an object to rotate when it is rotating x distance from the centre of mass?

Last edited: Nov 22, 2013
4. Nov 22, 2013

### jbriggs444

It is a measure of how easy it is for an object to rotate about a specified axis.

It is based on how easy it is for a point mass at distance x from an axis to rotate about that axis. You add up the "how hard it is" for every point in an object and that's the moment of inertia.

Often, the axis will be taken to be the object's center of mass. But it does not have to be. You can compute the moment of inertia of a stick about its center or its moment of inertia about one end.

5. Nov 22, 2013

### Panphobia

Ok now that makes sense, thank you both!

6. Dec 27, 2013

### shaunakm

I actually wanted to know the condition for toppling of a body on a horizontal rough surface ..
Plzz help