Wednesday, April 6, 2011

5 cm per second

Sometime ago, Nirbheek recommended me a anime movie which I watched and liked a lot.
It was named 5 centimeters per second and it is currently my favorite anime movie of all times. Quoting from Wikipedia:
The title 5 Centimeters Per Second comes from the speed at which cherry blossoms (also called Sakura blossoms) petals fall, petals being a metaphorical representation of humans, reminiscent of the slowness of life and how people often start together but slowly drift into their separate ways

And I remember this fact from the movie well. Also, I was until very recently, in Japan and I missed the Sakura blossoms (and the calamity) by a whisker (about 3 weeks).

So on my way back from EPFL, these Cherry Blossom trees took me right back:

Cherry blossom at EPFL

And I was immediately taken back to the same streets I had walked back in Japan, and woe fell unto me when I thought that I will never be able to see the Cherry blossom fall at the rate of 5 centimeter per second.

As this nostalgic mood was about to overwhelm me, I sought to engage myself with other questions, for example, how did Akari find out that cherry blossom falls at 5 cm/second? Well, she must have read it someplace, or maybe performed an experiment herself. After all, all it will take is a meter scale, a stopwatch and Cherry blossom petals to find out. Of course, in the absence of any other information, one would assume that the leaves were falling in a still air atmosphere.

And since I had all the requirements of the experiment, including the Cherry Blossom tree, I can verify her claim! So I promptly went back to the tree and got myself a handful of Cherry Blossom flowers:
Sakura leaves

Then I borrowed a meter-rule form my neighbor, marked a height of 120 cm, and set about the experiment:
A Cherry blossom petal and the 120 cm mark
I took care to shake the leaves loose instead of pulling them apart. Then I collected 22 readings, after which, the leaves looked remarkably shaken up:
Shaken up Cherry blossom, aptly kept atop Statistical Signal Processing and Applications

While some leaves fell quickly, others took their time in cruising along. By visual inspection I was able to tell that the leaves reached their terminal velocities during the fall.  I also took care to allow the leaves to fall without touching any thing on its way down:
Cherry Blossom petals lying on the floor of my room


The leaves fell with a speed of 78.4 cm/s ± 4.6 cm/s.

This is significantly (an order of magnitude) different from the 5 cm/s estimated by Akari.


  1. I understand why Charles Babbage suggested Alfred Lord Tennyson change the few lines in his "otherwise beautiful poem".
  2. Please do not take this to be a sign that the movie is not good. However, you will be correct in expecting that the movie is not scientifically very rigorous.
  3. This guy is correct.
But, still, watch it.

This is how fast you fall in love.

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