The figure shows a model for the motion of the human forearm in throwing a dart. Because of the force M→ applied by the triceps muscle, the forearm can rotate about an axis at the elbow joint. Assume that the forearm has the dimensions shown in the figure and a moment of inertia of 0.065 kg·m2 (including the effect of the dart) relative to the axis at the elbow. Assume also that the force M→ acts perpendicular to the forearm. Ignoring the effect of gravity and any frictional forces, determine the magnitude of the force M→ needed to give the dart a tangential speed of 3.6 m/s in 0.15 s, starting from rest.
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.
The figure shows a model for the motion of the human forearm in throwing a dart. Because of the force M→ applied by the triceps muscle, the forearm can rotate about an axis at the elbow joint. Assume that the forearm has the dimensions shown in the figure and a moment of inertia of 0.065 kg·m2 (including the effect of the dart) relative to the axis at the elbow. Assume also that the force M→ acts perpendicular to the forearm. Ignoring the effect of gravity and any frictional forces, determine the magnitude of the force M→ needed to give the dart a tangential speed of 3.6 m/s in 0.15 s, starting from rest.
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