how fast does earth have to spin?

I'm not going to calculate this, but I will tell you there is no way for the Earth to spin fast enough to send someone off into space at escape velocity. Once the centripetal acceleration exceeds gravitational acceleration, the false force created by your inertia might throw you into the air - but you would just bounce back down again.

Unless the Earth were spinning once about every 3,000 seconds, or 50 minutes, then it could fling you off into space - but only if you manage to stand on the Earth in the first place, and remain in the same spot so that you reach 11.2 km/s. And even then the atmosphere would instantly kill you, assuming it was still there, or at least induce drag causing you to fall many kilometers to a grisly death on a hellacious, spinning-too-fast planet.

Also it doesn't matter how much something weighs. If you're trying to get rid of your kid, you might find yourself flung into space instead.

I hope you're not planning to accelerate the Earth, if so, your evil plan must be stopped.

There is no such thing as the "centrifugal force". It isn't a force, it is an effect. It is an illusion of a force toward the outside of a rotating reference frame.

Also, if Earth were spinning this fast, no child would weigh 100 lbs. Every object would be weightless on Earth's equator. You could say that the child has a mass of 100 lbm (mass basis pounds) instead. It actually will NOT matter what the mass of the object is.

The calculation is such that you equate the equatorial true gravitational field (as found by Newton's law of gravitation) to the centripetal acceleration of a body on Earth's equator. The equatorial true gravitational field is the gravitational field at the equator as if the Earth weren't rotating, and would be dosido-ing as observed relative to distant stars.

I've done the calculation before, and it seems that Earth would need a sidereal period of revolution of about 55 minutes for this condition to occur.

Do realize that if Earth were to spin this fast, its body would bulge at the equator to the extremes, and the equatorial radius would no longer be what it is now.

No, a nuclear explosion ,like the different, has symmetry, it has rigidity equivalent in all guidelines, so any rigidity encouraging spin could be counter balanced via rigidity discouraging spin, they are going to be equivalent and cancel (except it became into some how shape chargd). besides, in comparison to different forces (like tidal rigidity of the moon) that is fairly negligible.The earth spins because of the fact momentum is left over from the formation of the image voltaic device, the earth used to spin quicker, the earths spin is slowing down, faster or later it is going to offer up spinning, or no longer, because of the fact the sunlight will great nova earlier this occurs.

To lift a child (or adult or elephant or battleship) off the ground it would have to spin round once every 1.5 hours.

To throw them off into outer space it would have to spin once per hour.

But you must realise that not only would the child fly off, but so would all the elephants, battleships, mountains, valleys, countries, oceans (and fish & whales)

In short everything would fly off till there was noe planet Earth left.

SO DON'T DO IT, Right? Alan

I beleive the escape velocity is 17,000 mph. The earth currently spins at 1,000 mph at the equator. So it would have to spin about 17 times faster than it does. That would mean a day would last roughly 1.5 hours.

The tangential speed would need to be at least escape velocity, which near Earth's surface is about 25,000 miles per hour. For a given angular rate of spin, the highest tangential speed is on the Equator. It so happens that Earth's equatorial circumference is about 25,000 miles, so it would need to spin at least at about one revolution per hour to allow an object on the Equator to be thrown off and never return.

I don't think the speed of the Earth spinning has anything to do with it. It's all to do with gravity. Gravity keeps everything here on Earth despite how fast Earth spins.