# Motion sickness

[SOLVED] Motion sickness

If the Earth were to stop dead in its tracks, (orbit/rotation), would its inhabitants notice the motion change?

Staff Emeritus
Gold Member
No, they'd all be dead by then.

Whatever it was that caused the 'stopping dead' would surely kill every living thing in seconds.

For example, a head-on collision with another Earth, orbiting the Sun in the opposite direction.

Clarification

I guess I am wondering if we would feel any motion change in the earth. How would the laws of motion apply to a change in motion of a celestial body and the effect of those objects and beings on it?

FZ+
Er... yes... the laws of motion are universal, as far as we can tell.

What is critical is how the Earth is stopped, and whether the inhabitants, the oceans etc are stopped with it...

I have read that we are traveling at nine miles per second if you combine our orbit around the sun, and our rotation around our axis. I can see people on one side of the planet being plastered to the earth, and others on the opposite side flying out into space along with a great bit of debri, both man made and natural. Is this a correct assumption?

Guybrush Threepwood
that is if the Earth doesn't break to pieces when it stops...

Staff Emeritus
Gold Member

... and the 'stopping' takes place in how many nanoseconds? ... and the boundary between what 'stops' and what doesn't is where?

We could go to Chicxulub to get an idea, and that was, what, a body of 'only' 10-n of the Earth's mass (anyone got a value for n?); and it happened in t >> 1 ns.

Not much flying and plastering I suspect, more like 'instant' vapourisation.

A question similar to this was posed in the old Forums. But that question was only asking about stopping the Earth's rotation on its axis. For the current discussion, rotational velocity is negligible since, even at its worst (at the equator), rotational velocity is only about 1,000 mph. Orbital velocity is something just over 40 miles per second! But, as I said in the old thread, it depends upon the mechanism that does the stopping.

If it were done mechanically, we would have some serious problems, that's the bad news. The good news is that only a fraction of a second later, we would no longer have any problems at all . For people on the "leading" edge (whose clocks read after midnight but before noon) there would be a brief but very interesting ride, as they found themselves launched suddenly from the ground. Those standing on the equator at dawn would be launched straight upward, while those at the polls, along with those who have just past midnight or are just shy of noon, would be launched straight sideways. Now, I was going to add that all of these people would instantly be vaporized by their impact with the air, but the truth is the atmosphere would probably leave with them. So they would find themselves propelled into space, where the atmosphere would rapidly dissipate, and they would all spend the last few seconds of their mortal existence sucking vacuum (and all that goes along with that).

Those on the "trailing" side of the globe (whose clocks read after noon but before midnight) would make impact with the ground beneath their feet at 40 miles per second. They would not even be a stain.

However, if this were done by an anomaly of rotating space-time, it might be possible for the event to pass utterly unnoticed. With no catastrophic change in momentum, and no measurable acceleration forces, the event could only be detected through observation of objects not affected.

Staff Emeritus
Gold Member
scifiman - Welcome to Physics Forums!

Just remember Newton's First Law of Motion (An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.)

Or think what happens to the occupants of a car that hits a brick wall (and then realize that a car is going in slow motion compared to the speed of the Earth).

TonySlim
you all may die, but the ladies and I would ride the atmosphere to mars, silver surfer style, and start our super-martian colony.

Staff Emeritus
Gold Member
Originally posted by TonySlim
you all may die, but the ladies and I would ride the atmosphere to mars, silver surfer style, and start our super-martian colony.

Everyone knows the leather goddesses are on Phobos. (anyone remember that game?)

I remember:

Macho chicks with guns

Bat-winged bimbos from hell

and, my personal favorite,