# Some Explanation about Momement of Inertia

1. Nov 17, 2009

### firoz.raj

Can anybody give Some Explanation about Momemet of inertia.Kindly let me know the idea
Any help would be highly appreciated.

2. Nov 18, 2009

### Lsos

It's how hard something is to spin.

It takes some force to make a merry-go-around...go around. It's because it has a sizeable moment of inertia. If you put some kids in it, it gets even harder to spin, because it has a greater moment of inertia. If all the kids go to the very edge of the merry-go-around, it gets EVEN harder to spinn.

So basically, how heavy something is and where this mass is located has an effect on moment of inertia.

The explanations go way deeper, but that's the simplest way to visualize it, imo...

3. Nov 18, 2009

### firoz.raj

Can you tell me the example of Moment of inertia in daily life .Describing Moment of Inertia.
Sorry don't mind .this is really silly question.But i will ask.

4. Nov 18, 2009

### Lsos

A merry go around is not good enough?

Ok...a door then. A heavier door is harder to swing open than a lighter door, because it has a greater moment of inertia. If you get someone to hang at the end of the door, the moment of inertia is even greater.

Or, try traking a heavy book or weight with each hand. Hold them close to your body, and try spinning around. Now spread your arms out (while still holding the weights) and try spinning. You'll notice it's harder to get yourself spinning with your arms spread out. While still spinning with your arms spread out, try bringing them in close to your body....you'll notice that your body will automatically try to spin faster. It's because it has the same energy (due to the spinning), but you're decreasing its moment of inertia by bringing your arms in. Same energy+lower moment of inertia=faster spinning.

Moment of inertia is the same thing as regular inertia (the heavier something is, the harder it is to get moving), except the motion applies to a spinning motion around an axis.

Last edited: Nov 18, 2009
5. Nov 18, 2009

### firoz.raj

Can you tell me .How will i calculate the Moment of Inertia.Kindly let m know the idea.
Additional Moment of Inertia also involve the Kinetic Energy .E=1/2mv.
Kindly let me know the idea.Any help would be highly appreciated.

6. Nov 18, 2009

### diazona

7. Nov 18, 2009

### Naty1

friz: You might also find this interesting:
http://en.wikipedia.org/wiki/Gyroscope

I've known about it for longer than I would care to admit and still find it fascinating. At first it seems to defy logic but is just one of many phenomena that physics can explain.

8. Nov 21, 2009

Thank You