For those of you who drive, you might have noticed this. You get in your car, start the engine, put it in first and start driving about 100,000 km/h backwards. What? You haven't noticed? You probably do it on a daily basis!

Let me explain. When you get in your car, and start driving, and reach the speed of 80 km/h, you accept the concept of relativity, because you are only travelling 80 km/h relative to the surface of the earth. If you wanted to be more precise, so that everybody on this planet can be using the same figures, you would calculate your speed relative to the center of the earth. This is not some weird thing to do, it actually makes more sense! So, it's an accepted fact that the earth rotates on it's axis, and completes one rotation is 24 hours. At the equator, the earth's circumference is about 40,000 km. After some simple math we decided that any point on the equator is moving 1,670 km/h eastward. That means if you drive east along the equator at your comfortable 80 km/h you are actually going 1,750 km/h. This is different as you move North or South of the equator because the circumference is shorter there, and it still takes the same time for one rotation. At 40 degrees North, driving east at 80 km/h, you would be going more like 1,360 km/h.

It gets better though. Actually we should be calculating our speed relative to the sun, because the earth is moving around the sun at about 107,000 km/h. So now, depending on how far North or South you are of the equator, and depending on the time of year, you could be moving at 107,000 km/hr plus or minus no more than 1,750 (That's more than 1,000 km/second!). Just sitting and reading this, you are moving at more than 100,000 km/h!

Source: http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit4/movearth.html