## Estimating the Distance of a Lightning Strike

###### By Anupum Pant

Everyone who’s studied basic science at school knows that light travels much much faster than sound. Light can travel about 300,000 km in a single second. Sound, in the same time would cover about 0.3 km. That’s a huge difference.

Considering that, it is fairly easy to calculate how far a lightning strike happens by measuring the time it takes the sound to reach you after you see the lightning. In that case, taking into account the enormous speed of light, you assume that the light instantly reaches you and you just count the seconds it takes for the sound to be heard at the place you are.

Then multiplying the seconds with 0.3 would give you, in kilometres, how far it happened – an estimation of, course.

So, if there isn’t a mess of lightning strikes happening somewhere, which usually isn’t the case, and if you can clearly tell which sound came from which lightning strike, which you can’t in most cases, you can actually estimate the distance of a strike very easily.

If you think that’s great. You might be interested in:
How to estimate the temperature.
and How to estimate the time to sunset.

## [Video] What Travels Faster Than Light

###### By Anupum Pant

Like always, another one of those awesome Vsauce videos where Michael explains how darkness and scissor intersections can travel faster than light and still not go against any physics laws. So much to learn! Let me just say nothing today.

P.S there’s a mention of the Dunning Kruger effect and the story of Mr. Mc Arthur Wheeler I covered some time back on the blog.

## 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…