The unit meter was defined with the second's pendulum as follows.        

        The length of the cord has a significant impact on the time required for each swing, While the mass of the bob has no effect, And the amplitude of the swing has only a minor impact. A little object called a bob is attached to a long cord in the simplest type of pendulum. The bob is little compared to the cord, And the cord is light compared to the bob. When pushed, The bob swings back and forth, And because no energy is lost due to friction or resistance, The amplitude of the oscillation remains constant.

            The explanation for this became obvious not long after calculus was discovered. When Newton's laws of motion were applied to the forces acting on a simple pendulum, A differential equation resulted.

Under the simplifying assumptions, The pendulum was found to have a time period of

T=2π/√(l/g)

Where T= time period,

l= length of the cord,

g= gravitational constant,

            The time period varies with the length “l” of the cord proportionally. This means if the length of the cord is increased, the time period will also increase. And time period will also be affected by the gravitational force on it. But, Gravitational force is inversely proportional to the time period (or) if the gravity increases, the time period will decrease. So, try substituting the values of gravitational force and time period as 1sec for half period. You will get a 1-meter value for the length of the cord.

            If you take the length of the cord in such a way that it will take 1 sec to make half period (the bob moves from left to right (or) right to the left). If you measure the length of the cord, it will be one meter. You can also say this; If you take a 1-meter cord, then under the earth gravity, it will take 1 sec to complete one swing (either from left to right (or ) right to the left).

            However, there were issues with defining the meter in this manner. To begin with, it would imply that the meter's definition was predicated on that of a time unit (the second), Making it a less than fundamental unit. Worse, a pendulum's period varies from place to place on the Earth's surface. To understand why to consider what Newton demonstrated; as you got closer to the Earth's center, The gravitational force, including your own weight, increases.

            If the gravitational acceleration increases by a certain percentage, The period of the pendulum drops by half that percentage. The length of a pendulum is proportional to its distance from the Earth's center. So a pendulum swings a little slower on a peak than it does down a neighboring shore. The impact of the planet's "equatorial bulge" is even more profound. According to Newton and Huygens, the Earth is a somewhat squashed spheroid due to the centrifugal force of its spinning.

            If, As Newton predicted, The planet's surface is an elliptical spheroid with an eccentricity of 1/230, the length of a pendulum would need to be altered greatly to have a 1-second swing at all locations. In 1735-1744, the French Royal Academy of Sciences sent surveying missions to Peru and Lapland to investigate this notion. The length of one degree along a meridian of longitude is longer near the Equator than near the North Pole, According to their land survey data. They were able to back up their claim by measuring how much slower a pendulum oscillated in the first site than the second.

            As it is impossible to achieve the same dimension at different locations. Meter dimensions were redefined in so many ways. But, That’s for another article; thanks for stopping by.