Why Don’t Humans Get Thrown Off the Surface of the Earth Due to its Rotation?

-- Peter | January 22, 2021

Question:

g’day there Jeff, please help me explain something easily for a 10 year old to understand, as my son asked me recently after we visited an amusement park during our xmas break ”why don’t we get thrown off from earths surface if its spinning at 1700kmh like as with some amusement park rides that spin very fast gravity(centrifugal force) tries to eject us out?’’ I did try explaining it but with my education & google’s abundant information I left him plus I slightly more confused & with only more questions than answers Doh! ): Appreciate any help you can give me very VERY much. Kind Regards; PJ.Harrison & HK.Harrison, Melbourne, AUS.

-- Peter

Answer:

The short answer is that the Earth’s gravity keeps us from being flung off into oblivion. To verify this, we can compare the outward acceleration that one feels due to the Earth’s rotation with the inward gravitational acceleration due to the Earth’s mass. The Earth rotates with a period of about 23 hours 56.07 minutes, or about 86164 seconds. The Earth’s equatorial radius of about 6378 km, so its circumference is 2*pi*radius, or about 40074 km. We can then calculate the velocity at the equator as circumference/rotation period, or 40074000 m/86164 seconds = 465.1 m/s. The centrifugal acceleration that one feels at the Earth’s equator using the equation (velocity)^2/radius is then (461.5 m/s)^2/6378000 m = 0.03 m/s^2. Compare this acceleration away from the surface of the Earth to that due to gravity, about 9.81 m/s^2, which is directed toward the center of the Earth. You see then that gravity wins, and that the Earth’s rotational motion reduces the affect of gravity by only about 0.3%.

-- Jeff Mangum

Facebook

Twitter

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
	Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.
	The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."
	AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.