a. A ball is dropped from the top of the building. Since the ball speeds up as it falls, the linear momentum of the system containing the ball and the Earth is not conserved. b. A wheel rotates counterclockwise in the xy plane. If the angular speed decreases over time, the angular acceleration vector points in the - Ê direction. c. A ball is suspended by a string that is tied to fixed point above a wooden block standing on end. The ball is pulled back as shown in the figure below. In trial A, the ball rebounds elastically from the block. In trial B, two-sided tape causes the ball to stick to the block. It is more likely that the ball knocked the block over in trial A than in trial B.
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.
State whether each statement is true or false and why.
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