When the pendulum bob reaches the mean position, the net force acting on it is zero. Why then does it swing past the mean position?
The reason a pendulum swings past the mean position even though the net force acting on it is zero at that point is due to the concept of inertia.
Inertia is the tendency of an object to resist changes in its motion, either to speed up or slow down. When a pendulum reaches the mean position, it momentarily comes to a stop before reversing its direction. At this moment, both the gravitational force and the tension in the string balance each other out, resulting in a net force of zero. However, the momentum of the pendulum bob causes it to continue moving due to its inertia.
When the pendulum bob is at the mean position, the velocity is momentarily zero, but the momentum (mass times velocity) is not. Therefore, the pendulum bob continues to move past the mean position due to its inertia. Once it moves past the mean position, the force of gravity acts on it again, accelerating it back towards the mean position, creating the characteristic swinging motion of a pendulum.
To calculate the force and motion of a pendulum accurately, one needs to consider the conservation of energy, the forces of gravity, tension, and friction, as well as the laws of motion. By applying these principles, equations like the equations of motion and energy conservation can be used to analyze and understand the behavior of a pendulum.