## Speed of the Earth in Space

In Lower Secondary class we are covering the basic formula Speed = distance /time.

**Lower Secondary Question:** Given that the earth is 150 million km from the sun, find the orbital speed of the earth around the sun in km/hr. Assume that the earth’s orbit is circular and take the year to be 365 days.

**Solution:** The circumference of a circle is given by 2(pi)r = 2×3.14×150×10^6km = 9.42 ×10^8 km. This is the distance that the earth travels in one year. Taking speed = distance/time

As a comparison the escape velocity of a rocket traveling to Mars only has to reach a speed of 45,000 km/hr to get away from the earth’s gravity. So the earth is moving very fast around the sun !