How fast would Earth need to spin for humans to be thrown into space?

If ever you needed an answer to get your head in a spin then this is the one.

26th September 2016
How fast would Earth need to spin for humans to be thrown into space? (Chris Philpot/BBC Focus)

Asked by: Daisy Clare, age 10, Swindon

Normally, humans aren’t thrown off the moving Earth because gravity is holding us down. However, because we are rotating with the Earth, a ‘centrifugal force’ pushes us outwards from the centre of the planet. If this centrifugal force were bigger than the force of gravity, then we would be thrown into space.

The strength of the centrifugal force depends on where you are. It is greatest at the equator and zero at the Earth’s poles. We can calculate how fast the Earth would need to spin to balance the force of gravity (this is known as the ‘escape velocity’). It works out at about 28,437km/h (17,670mph). The Earth would have to spin once every 84 minutes to achieve that speed at the equator, or about 17 times faster than it actually spins. If you move away from the equator the centrifugal force is lower so you still wouldn’t fly off into space, even at that speed. At the latitude of Swindon, for example, the Earth would need to rotate once every 52 minutes to throw the resident humans off into space. 

 


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