Question

What is the distinction between inertial mass and gravitational mass? Why is it surprising that they are the same?

Answer 1

Inertial Mass - It is calculated applying a known force and measuring it's acceleration and then using Newton's Second law as m = F/a [where F = force, a = acceleration and m = inertial mass]

Gravitational Mass - It is calculated by it's gravitational force of attraction for other bodies. We can also say, it is the property of a body which causes it to have weight in gravitational field.

m = Gravitational force / acceleration due to gravity.

As, both the equations looks like, mass = Force/acceleration, so inertial mass and gravitational mass have always same value.

Both the laws are given by Newton.