Final answer:
A pivot point is a center of rotation, like a shoulder for arm movements. In this physics context, the shoulder acts as the pivot for calculating torque involving muscle force exerted, considering the arm's lever arm and the force of gravity on an object held in the hand.
Step-by-step explanation:
The pivot point around which the arms move is the point on the body, such as the shoulder, that acts as the center of rotation for the movement of the arm. Based on the information provided, if the muscles exert a force causing the arm to rotate with the ball 0.600 m from the pivot at the shoulder, and their effective perpendicular lever arm is 4.00 cm, we can calculate the necessary force exerted by the muscles.
To calculate the force, we need to consider the concept of torque. Torque (τ) is the product of the force (F) applied and the perpendicular distance from the pivot point (r), i.e., τ = F * r. The perpendicular distance or the lever arm is given as 4.00 cm or 0.04 m, and the force exerted by the ball due to gravity is the product of its mass (0.156 kg) and the acceleration due to gravity (9.81 m/s²). We can then use this to find the force applied by the muscles by rearranging the torque equation to solve for F.
Keep in mind that there are several aspects to consider when solving these kinds of problems, such as choosing the appropriate pivot point, which often simplifies the calculation of torques.