You are already moving very fast
What If the Earth Stopped Spinning?
The problem is not that you would stop. It is that you would not.
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Step 1 of 5
You are already travelling at enormous speed.
Speed is only noticeable when something nearby disagrees with it. Stand at the equator and you are being carried east at about 1,670 kilometres an hour. You cannot feel it because everything around you — the air, the sea, the ground — is going exactly as fast.
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Step 2 of 5
Stopping the ground would not stop you.
A moving thing needs a reason to stop. The ground stopping is not one. Anything not bolted down keeps its speed: people, cars, buildings, and the entire atmosphere. The air alone would arrive as a permanent 1,600 km/h wind, which is roughly five times a hurricane.
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Step 3 of 5
The sea would slide off the middle.
Spinning is what holds the ocean in a bulge round the equator. Take the spin away and the water runs downhill towards the poles. That leaves a belt of dry land all the way round the middle, and two enormous new oceans at the ends.
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Step 4 of 5
One day would last one year.
The Sun still crosses the sky. It just takes a year to do it. The Sun would still go round the sky, because Earth would still be going round the Sun — just once a year instead of once a day. Six months of daylight, then six months of night, everywhere.
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Step 5 of 5
It is very slowly happening anyway.
The Moon is dragging on our tides and stealing a little spin every year. Days are getting longer by about two thousandths of a second per century. When dinosaurs were alive a day was roughly twenty-three hours.
Coral fossils record this. Old corals laid down about 400 daily growth lines per year instead of 365.
The short version
The danger of Earth stopping is not stillness — it is that everything loose on it would keep going at 1,600 km/h.
Try it yourself
Slide a coin across a magazine, then stop the magazine suddenly. The coin carries on. That is you, if Earth stopped.