In a long jump, an athlete leaves the ground with an initial angular momentum that tends to rotate her body forward, threatening to ruin her landing.To counter this tendency, she rotates her outstretched arms to “take up” the angular momentum (Fig. 11- 18). In 0.700 s, one arm sweeps through 0.500 rev and the other arm sweeps through 1.000 rev.Treat each arm as a thin rod of mass 4.0 kg and length 0.60 m, rotating around one end. In the athlete’s reference frame, what is the magnitude of the total angular momentum of the arms around the common rotation axis through the shoulders?
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.
In a long jump, an athlete leaves the ground with an
initial
threatening to ruin her landing.To counter this tendency, she rotates
her outstretched arms to “take up” the angular momentum (Fig. 11-
18). In 0.700 s, one arm sweeps through 0.500 rev and the other arm
sweeps through 1.000 rev.Treat each arm as a thin rod of mass 4.0 kg
and length 0.60 m, rotating around one end. In the athlete’s reference
frame, what is the magnitude of the total angular momentum of the
arms around the common rotation axis through the shoulders?
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