why does the earth rotate and revolve
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? 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, only the relatively weak tidal forces from the Moon act to slow it down. This page was last updated on June 27, 2015.
If you have seen any of the films taken by the astronauts in outer space, you know that the earth spins. It spins so slowly that living here, we donвt even notice it. The spin is in a counter-clock-wise direction (backwards from the direction of a clock) and the funny part is: almost all of the planets in our solar system spin in the same direction. To understand why the earth spins, we have to go back in time to see how our solar system was created. In the deep reaches of space, gas and dust clouds form in what is called a вnebulaв. These are the birthplace of stars. As they swirl and spin the dust collects together and pressure builds up. Like shaking up a soda can, when the pressure is released, it sprays out. In the case of a nebula, it can create stars.
Itвs also thought that it takes a special event, like the explosion of another star going вnovaв to finally blast everything out. The explosion causes the star and all of the dust and dirt to spin. Since everything was hit in the same direction from the explosion, they spin in the same direction. Thereвs so much dust that has gathered together that pieces begin to slam into each other, eventually forming asteroids and these are pulled in by the gravity of the spinning star. This goes on for billions of years, with everything bumping and crashing together. Bigger and bigger pieces are formed as the asteroids collide and stick together, all the while they are all spinning in the same direction. Remember that star that was created? Well, it has gravity that slowly pulls all of the asteroids, dust, dirt and everything else in towards it. This process creates even more collisions until finally they form what will be planets. In almost all cases, even crashing into each other doesnвt change the direction that they are spinning. Thatвs how powerful the explosion was. The star that is in the center of all of this chaos, is becoming a future sun. But it doesnвt settle down quite yet.
During this time, the future вplanetsв are circling around this new sun, but things are still quite unstable. As they cool and spin, they can also collide into each other, forming bigger planets, with the left over pieces forming what will be moons. The gravity of the sun continues to pull for billions more years until the planets settle into their rotation around the sun, leaving plenty of room for each other so they donвt collide. If we had been out in a spaceship, watching all of this happen, we would notice that all of the planets are still spinning in that same original direction. Some spin faster than others, but all are spinning and slowly circling around the sun in their own path. We would also see the various moons around the planets. These can spin in the same direction as the planet or completely opposite, because they were created after the original explosion. So we can say that the earth is spinning because it was part of an explosion that caused the birth of our sun and solar system and that explosion was so incredible that it has kept the planets spinning. Since there is nothing to stop it, the earth will continue to spin. Useful Websites NASA - archive. org -
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