You hold a softball with a weight of 1.80 N in your hand as shown in the figure. Your arm is moving, but at the instant shown, your arm is horizontal. Consider your forearm and hand to be a uniform rod with a mass of 1.65 kg and the distance between your elbow joint and the ball in your hand is 2L = 26.0 cm. Your biceps exerts an upward, vertical force of 13.5 N on your forearm and is attached a distance of d = 2.60 cm from your elbow. (a) Using your elbow joint as the axis of rotation, determine the magnitude of the net torque acting about your elbow due to the weight of your forearm/hand, the weight of the ball, and the force applied by your bicep. N · m (b) In which direction will your forearm and hand rotate, given the signed value of the net torque calculated in part (a)? clockwise counterclockwise no rotation
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.
You hold a softball with a weight of 1.80 N in your hand as shown in the figure. Your arm is moving, but at the instant shown, your arm is horizontal. Consider your forearm and hand to be a uniform rod with a mass of 1.65 kg and the distance between your elbow joint and the ball in your hand is
Your biceps exerts an upward, vertical force of 13.5 N on your forearm and is attached a distance of d = 2.60 cm from your elbow.
N · m
(b) In which direction will your forearm and hand rotate, given the signed value of the net torque calculated in part (a)?
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