Lower Part of a Wheel Travels Slower

By Anupum Pant

Stick a colourful piece of paper on the side of a rim of a wheel and make the wheel roll away. If you observe carefully you’ll see, whenever the paper is near the ground, it appears clearly. However when the paper is at the top of the wheel, furthest from the ground, the paper appears hazy.

Also if you observe the spokes of a wheel of a moving cart, you’ll see that the spokes at the lower part of the wheel appear clearly. While the spokes of the upper part appear to blend into a single body, as if travelling much faster than the lower part.

It seems, the upper part of the wheel is travelling at a higher speed than the lower part of the wheel. How can that be, when both are physical extensions of a single object?

Yes, in fact the upper part does travel faster than the lower part. This sounds incredible, while it seems very ordinary to others who understand the simple physics of it. The physics involved really is very basic. So basic that I’m sure many reading this are cursing me for writing something so ordinary. But I find it really incredible. And believe me, there still are people who need to know this.

Let’s suppose the wheel moves at a speed of v in the right direction. However that is just the speed of the centre of the wheel. The upper part of the wheel for instance rotates at a speed of, say v, and also translates in the same direction at a speed of v. So, the speeds add up. And the top is travelling at a speed of 2v.

Similarly, at the bottom part of the wheel, the rotation is in the opposite direction (towards the left) and translation is in the right direction. Hence the speeds get cancelled and the lowest part of the wheel is stationary.

These are the topmost and bottommost points I’ve discussed here. For all the other points on the rim the rotational speed v gets split into a horizontal and a vertical component. So their speeds vary and lie in between 0 and 2v.

Some call it the cartwheel riddle.

Now, if you already knew that there’s something mind-boggling for you here. There’s another similar thing about wheels which blows my mind. Demonstrated in the video below…

Wiping Sparrows Resulted in 20 Million Dead People in China

Background

Starting from the year 1958, Mao Zedong wanted to rapidly transform the People’s Republic of China from an agrarian economy to a communist society through rapid industrialization. So, he introduced a huge economic and social campaign which aimed to make this transformation possible. It was called the Giant Leap Forward. However, the campaign ended in a massive catastrophe which resulted in the death of about 10 Million people (estimates range from 18 to 45 Million deaths). Mostly because Mao decided to mess with mother nature and created a serious ecological imbalance.

One integral part of the campaign was called the four pests campaign. The aim of this campaign was to exterminate four kinds of pests identified by Mao Zedong which would have, according to him, fixed their poor grain output in China. The identified pests were – Mosquitoes, Flies, Rats and Sparrows.

The Great Sparrow Campaign

Of all, Sparrows were considered as pests because the bird species was responsible for pecking on the grains produced by hard-working peasants. That was completely unacceptable to them. The Chinese solution – Kill all birds.

This part of the four pests campaign was known as the Great sparrow campaign. To wipe off all the sparrows, masses across the country were mobilized. Some shot birds from the sky. Others just banged metal plates when they saw sparrows. Sparrows were not allowed to rest. As a result, flying sparrows fell down out of exhaustion. There were incentives according to the volume of pests people got rid of. It was brutal.

The Ecological Imbalance

The extermination of “pests” was expected to bring about a better output in grains, but it resulted in something totally opposite. Moreover, the results of this campaign were totally devastating.

As all the sparrows were being killed, there was a serious ecological imbalance. Now, there were no sparrows left to eat the quickly multiplying insects. It resulted in the rise of real pests (insects) like swarms of locusts etc. Instead of seeing a rise in the grain yeild, China saw a drastically decreased yeild.

The Great sparrow campaign ended up being  a major factor that contributed towards the Great Chinese famine in which about 20 Million people died out of starvation.

Moral: You don’t mess with mother nature.