Question

Two spherical bobs, one metallica and the other of glass, of the same size are allowed to fall freely from the same height above the ground. Which of the two would reach earlier and why?

Answer 1

Hint: In this question use the concept of insulators and conductors as insulators do not experience any field but conductor’s experience the magnetic field of the Earth when it falls freely from the same height so use these concepts to reach the solution of the question.

Complete Step-by-Step solution:
As we know glass bob is non-conducting in nature as this an example of insulator on the other hand metallic bob is conducting in nature as this is an example of conductor.
So if these two bobs fall freely from the same height they both experienced the Earth gravitational pull.
Not due to the conducting nature of metallic bob it also experienced Earth magnetic field because when metallic bob fall freely from some height eddy current is induced by the metallic bob as it falls through the magnetic field of the Earth.
So According to Lenz’s law, the induced current is such that it opposes the free falling motion of the metallic bob and it experiences an upward force.
This will slow down the speed of metallic bob by some extent.
But due to the non-conducting nature of glass bob, glass bob does not experience any kind of such forces so glass bob only experiences Earth gravitational pull.
Hence glass bob will reach the earth before the metallic bob.
So this is the required answer.

Note – An interesting fact is that when these two bobs falls freely in normal condition glass bob reaches the Earth first as explained above but if hypothetically there was no magnetic field and no air resistance (vacuum), then both bobs will reach the ground at the same time because initial velocity is 0 and the acceleration due to gravity is independent of the bob’s mass.