Why do Planets Spin?

by | Apr 20, 2018


Earth spins at 1,040 miles per hour. The other planets in our Solar System spin as well:

  • Mercury, 7 mph
  • Venus, 4 mph
  • Mars, 538 mph
  • Jupiter, 28,262 mph
  • Saturn, 22,994 mph
  • Uranus, 5,544 mph
  • Neptune, 5,143 mph
  • Non-planet Pluto, 29 mph

Why do they spin? Post-Big Bang planets and stars formed inside giant interstellar clouds of gas and particles. As these clouds cooled particles of matter were drawn together and collided. As smaller pieces of matter joined larger pieces of matter the new particles joined from different angles. This caused the spin, similar to one cue ball hitting another at a glancing angle and causing the hit ball to spin. The mass of the new planets grew as particles continued to join, gravity increased and caused the particles to condense. The condensing of the mass caused the spin to increase in speed similar to what happens when a figure skater pulls in her arms to spin faster. This is why the larger planets spin faster than the smaller ones.

The planets keep spinning due to inertia. But they are slowing down. When Earth was first formed a day was just 5.5 hours long. The Earth is continuing to slow down and our days are getting longer. IFOD on this: Days are getting longer

Due to spin of the Earth, someone who weighs 150 lbs at the poles would weigh slightly less – 149.2 pounds at the equator due to the centrifugal force counteracting a bit of Earth’s gravity.

Related IFOD on formation of stars: A Star is Born


  1. Not only the centrifugal force affects measurements, there’s also the Coriolis force. (Neither are true forces – they are just the result of being in or moving relative to the earths spin and gravity)

  2. So, if weight is different at the Equator from the Poles due to gravity being affected by centrifugal force, then I’m assuming this would affect other measurements. Can barometric pressures, temperatures and ozone levels be affected merely by the affect of centrifugal forces?
    Just curious, these are the things that keep me up at night….and my calico cat who demands me to awaken and feed her in the middle of the night.


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