If you toss a textbook into the air, rotating it each time aboutone of the three axes perpendicular to it, you will find that it will not rotate smoothly about one of those axes. (Try placinga strong rubber band around the book before the toss so thatit will stay closed.) The book’s rotation is stable about thoseaxes having the largest and smallest moments of inertia, butunstable about the axis of intermediate moment. Try this onyour own to find the axis that has this intermediate momentof inertia.
Angular Momentum
The momentum of an object is given by multiplying its mass and velocity. Momentum is a property of any object that moves with mass. The only difference between angular momentum and linear momentum is that angular momentum deals with moving or spinning objects. A moving particle's linear momentum can be thought of as a measure of its linear motion. The force is proportional to the rate of change of linear momentum. Angular momentum is always directly proportional to mass. In rotational motion, the concept of angular momentum is often used. Since it is a conserved quantity—the total angular momentum of a closed system remains constant—it is a significant quantity in physics. To understand the concept of angular momentum first we need to understand a rigid body and its movement, a position vector that is used to specify the position of particles in space. A rigid body possesses motion it may be linear or rotational. Rotational motion plays important role in angular momentum.
Moment of a Force
The idea of moments is an important concept in physics. It arises from the fact that distance often plays an important part in the interaction of, or in determining the impact of forces on bodies. Moments are often described by their order [first, second, or higher order] based on the power to which the distance has to be raised to understand the phenomenon. Of particular note are the second-order moment of mass (Moment of Inertia) and moments of force.
If you toss a textbook into the air, rotating it each time about
one of the three axes perpendicular to it, you will find that it will not rotate smoothly about one of those axes. (Try placing
a strong rubber band around the book before the toss so that
it will stay closed.) The book’s rotation is stable about those
axes having the largest and smallest moments of inertia, but
unstable about the axis of intermediate moment. Try this on
your own to find the axis that has this intermediate moment
of inertia.
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