Charged Pendulum in an Electric Field

As you learn physics, you might mistakenly think that different concepts have hard boundaries; for example, many people think that classical mechanics is classical mechanics and electromagnetism is electromagnetism. The two subjects must be studied separately, and they only overlap in certain special cases.

However, this is not true. Every physics concept that you learned in the past can be used to solve new problems - even if it looks like the domain is different. In this example I show how an electrostatics problem is solved using free-body diagrams (usually learned in classical mechanics). If you replaced the electric force (\(\vec{F} = q\vec{E}\)) with an equal tension force pulling the ball to the right, you would get the same answer for \(\theta\).

Forces on Charged Particle in Two Different Situations