## How do we know how fast planets are rotating?

Planets revolve around their axis.

But how do we, sitting on earth know how rapidly a planet like Mercury which is around 48 million miles away is rotating ?

## Doppler effect

This is a very interesting example of Doppler effect.

Radio waves are shot from the earth towards the surface of mercury, one side of the planet will be red shifted (since it is moving away from you) and the other will be blue shifted (since it is moving towards you).

By measuring this apparent change in frequency, we can find out how rapidly mercury is rotating.

Using this method we have found out that the rotation period of mercury is approximately 58.6 days.

Thanks for asking rj1124a@a! Great question!

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## Meet SAW (or Single Actuator Wave-like robot). A bioinspired…

Meet SAW (or Single Actuator Wave-like robot). A bioinspired robot that can move or swim forward and backward by producing a continuously advancing wave.

## Alternating wave pattern on Ropes

I saw someone working out with Battle Ropes the other day and this wonderful pattern emerged was absolutely fascinating. Of course, the waveforms are not purely sinusoidal but it helps us to understand why you see such patterns

## Perturbations in the field.

Perturbations in the field.

## The simple harmonic oscillator

Okay Anon! Here you go, this is my rendition.

## The problem

You have a mass suspended on a spring. We want to know where the mass will be at any instant of time.

Describe the motion of the mass

## The physical solution

Now before we get on to the math, let us first visualize the motion by attaching a spray paint bottle as the mass.

Oh, wait that seems like a function that we are familiar with – The sinusoid.

Without even having to write down a single equation, we have found out the solution to our problem. The motion that is traced  by the mass is a sinusoid.

## But what do I mean by a sinusoid ?

If you took the plotted paper and tried to create that function with the help of sum of polynomials i.e x, x2, x3 … Now you this what it would like :

By taking an infinite of these polynomial sums you get the function Since this series of polynomial occurs a lot, its given the name – sine.

I hope this shed some light on the intuition of the SHM equation. Have fun!