What makes the Earth rotate?
As a father and a science lover I was dumbfounded when my 7yr old son asked me "What makes our earth turn (rotate) ? He then asked "Did it start a long time ago and it just keeps turning or is something pushing it to turn"? How does the Earth continue to rotate around its axis? Where does the energy to keep it moving come from?
Our everyday experience teaches us that an object must be "pushed" by a force in order to keep it moving. Otherwise, it will slow down and eventually stop. But this intuition is absolutely wrong. If an object is moving, then a force is required *to slow it down or stop it*, not to keep it moving. (Hence, "Objects in motion tend to stay in motion. Objects at rest tend to stay at rest.") In our everyday experience, it's the force of friction that tends to stop Earth-bound objects from moving forever. But for the Earth rotating on its axis, there is no force working to counteract the rotation (except the tidal effect of the Moon, but that's working very slowly), so you don't need to have any input energy to keep it spinning.
What started the earth rotating in the first place?
Laura The shortest answer is angular momentum. Angular momentum is simply the name we give for the fact that things tend to rotate. (Just like regular momentum is the tendency for things to move.) The Earth formed out of a nebula that collapsed. As the nebula collapsed it began rotating, which may seem odd, but actually not rotating is far stranger than rotating. The Earth's rotation comes from the initial tendency to rotate that was imparted on it when it formed, and there is nothing (other than the tidal forces of the Moon, which are weak) to slow it down. (See above.)
Get More 'Curious?' with Our New PODCAST:
- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.
- Why do planets rotate?
- What would happen if an impact caused Earth to stop rotating?
- Is the Moon moving away from the Earth? When was this discovered?
- Since Earth is spinning, why do we land in the same place when we jump or fall?
- Does the Sun rotate?
- How can we tell what the interiors of planets are like?
How to ask a question:
If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist
This page has been accessed 244305 times since October 23, 2002.
Last modified: April 27, 2012 7:55:24 PM
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.
Warning: Your browser is misbehaving! This page might look ugly. (Details)