Do you feel the world as it really is? 107,000km/hr!

13 September 2011

The sun slowly sets and the seasons change even more slowly. Yet these things happen by us traveling mind-bogglingly fast in space and we don't even notice.

Most of us know that the earth rotates on its axis and that the earth also oribits the sun. You know – those slow old elephants of the solar system plodding away in space. Really? Have you stopped to think how fast we must be ripping along in space to get right around the whoppingly huge sun at a significant orbit distance (even though its takes a year)? Let's do the maths.

Circumference = 2 x π x radius (approximating our orbit from an ellipse to a circle)
Speed = distance ÷ time

Therefore, the speed of earth around the sun:
= (2 x π x orbital radius in km) ÷ (365.26 days)
= (2 x π x 149600000 km) ÷ (365.26 x 24 hours) 
= 107,225 km/hr
= 30km/sec

So let's get a feel for just how fast we're moving through space. The speed of sound is 0.343 kilometres per second. That means we are travelling at 87 times the speed of sound (30km/s ÷ 0.343km/s). That is fast! Of course there is no air in space and so you can't have sound since there is no medium for the compression waves to travel through. But you get the idea! We are absolutely ripping along all the time through our solar system just to get around the sun every year. The seasons seem to go very slowly but we are moving very very very very quickly!!! We don't feel it because there is no acceleration. Like moving in a train on a perfectly smooth track, we can walk back and forth without even feeling the journey at all.

It is hard to grasp that we are travelling 87 times faster than the FA18 Hornet in the picture below!! Mind you, since the plane is on earth, it's also traveling that fast. As it breaks the sound barrier relative to the ground, water droplets form from the drop in pressure behind the sonic boom shock wave and the result is the cloud that is shown (source). We are going 87 times faster than the FA18's already very fast speed. We would pass the FA18 so quickly that you could barely see it at all.

If you do the maths on how fast you move at the equator by the earth's rotation then it works out to be:

Speed at equator from rotation of earth
= (2 x π x radius in km) ÷ (24 hours)
= (2 x 3.14159 x 6378.1) ÷ (24) km/hr
= 1669.8 km/hr
= 464 m/sec

So if you are on the equator, you move faster than the speed of sound, just by the rotation of the earth on its axis!

The anti-speeding campaign in Australia used to ask the question "How fast are you going now?" Well the answer is 107,000km/hr! But don't tell that to the policeman – he might not appreciate the science at that time!