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Physics/End the debate


QUESTION: Why don't they ?

To end the ridiculous debate of whether or not the earth is spinning, why don't they just shoot bullets east and west.  Bullets hit targets higher shooting east and lower shooting west, right ?


Interesting, I didn't know there was a debate about that. Definitely a ridiculous debate, if it exists. About shooting bullets east and west, that would not resolve the issue. Bullet velocity is with respect to the muzzle it was shot out of. And the revolution of the earth carries the muzzle to the east just as fast as it carries the target to the east. So the time to the target would be the same whether the shot is to the east or to the west.

But if you shot the bullet north from the equator, and if it was a long-range shot (perhaps 1000 km), the Coriolis effect could be detected which would give evidence of the rotation. Reference:

I hope this helps,

---------- FOLLOW-UP ----------

QUESTION: Using equal measured bullet weight and muzzle exit velocity at the equator, a target 1 mile away east of the laser levelled gun, due to the spin of the earth the target is moving upward towards the gun therefore the bullet will hit lower than the bull's-eye where it is laser aimed.  A target west of the gun is moving down due to the spin of the earth therefore the bullet will hit higher than where it is aimed.

Is this not absolute proof that the earth is spinning ?

Hello AL,

OK, I now see what you meant in your first question. So let's study this proof you have proposed. We would have to assume several things (like no air drag) to allow you to discount other explanations for any discrepancy in where the bullet hit the target. I will allow all those assumptions for the sake of the study. But first I have to disagree where you say "the target is moving upward". If the target is east of you, it is moving downward. If you look to the east at sunrise, the sun is higher in the sky for those to the east of you.

Let's assume a muzzle velocity of 0.5 miles/second. So it will take 2 seconds for the bullet to reach the target. The circumference of the earth at the equator is 24,900 miles. In 1 hour, a point on the surface moves 15 degrees which has an arc-length of 1037.5 miles. In 2 seconds, a point on the surface moves 2*15/3600 degrees, or 0.008333 degrees, which has an arc-length of 2*1037.5/3600 miles, or 0.5764 miles. So the target will be only 0.4236 miles away when hit. I am using several approximations in the next steps, but I think they will yield an approximation of the distance that the perfect shot will miss the bulls-eye.
sin(0.008333 degrees)*1 miles = 0.7679 ft (converted from miles to feet)
sin(0.008333 degrees)*0.4236 miles = 0.3253 ft
0.7679-0.3253 = 0.4426 ft or 5.3 inches above the bulls-eye.

Is this not absolute proof that the earth is spinning ? I would expect anyone looking at this critically would challenge the idea that all sources of error were overcome. But yes, if you could answer all challenges, I would agree.

I hope this helps,


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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