WORLD OF FIGURES: Why cant we feel Earth’s motion as it goes around the sun?

Passengers look at a "digital earth" displayed at Kuala Lumpur International Airport (KLIA) in Sepang, outside Kuala Lumpur on March 16, 2014. After reading last week’s article about the motion of the Earth around the sun, several readers have asked a follow-up question: at what speed does it move? AFP/PHOTO 

8.07.2017

Summary

• Then yet another question arises: what keeps the Earth in motion? Well; the answer is also another question.
• What would stop it from moving? There is nothing in outer space to slow it down.
• Again; we are so accustomed to seeing moving objects slow down to a stop that we hardly ever ask what is slowing them down.

After reading last week’s article about the motion of the Earth around the sun, several readers have asked a follow-up question: at what speed does it move?

The numbers are easy to work out: the Earth is about 150 million kilometres from the Sun and it moves in a circular orbit. The distance around this circle is, therefore, “2-pi-R”. That is; 2 x 3.14 x 150,000,000 = 942 million kilometres.

Now this journey takes one year, or 365.25 days. That is 8,766 hours. So, the speed of the planet is simply the total distance divided by the time taken. The answer comes to 107,460km/h. That’s very fast. Commercial passenger jumbo jets cruise at an average of about 1,000km/h; so the Earth is hurtling at over 100 times the speed of an aeroplane. The question then arises: why don’t we ever “feel” this motion?

Well; the answer is in that last paragraph! Anyone who has ever flown in a jumbo jet will confirm that you don’t feel its motion even when it’s doing over 1,000km/h. Similarly, passengers who have taken a ride in our new Madaraka Express train are all saying it is so smooth that you can’t tell it’s cruising at over 100km/h.

We have become so accustomed to moving in road-based vehicles that we assume that motion should always be felt. The only reason we feel it is that the surface is quite rough. And I’m not just talking about potholes – a “smooth road” is not smooth at all!

Now; in outer space, there is no surface: the Earth just “floats”. And before some one asks me why it doesn’t fall off, let me ask: where would it be falling to? There is nowhere to fall! But that’s not entirely correct. There is one place that the Earth could fall: onto the Sun. It doesn’t fall there because it is in constant orbital motion. That motion counteracts the gravitational pull of the sun keeping our planet a safe distance away.

Then yet another question arises: what keeps the Earth in motion? Well; the answer is also another question. What would stop it from moving? There is nothing in outer space to slow it down. Again; we are so accustomed to seeing moving objects slow down to a stop that we hardly ever ask what is slowing them down. We assume that it is “natural” for things to slow down.

The truth is that things slow down because of the roughness of the surfaces that they are moving on and the resistance of the fluid (air, water etc.) through which they are passing. Since outer space is a vacuum, there is nothing to slow down the earth.

Finally: what set the Earth in motion? Scientists believe it was born that way - moving! There was never a time when it was stationary.

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