# Optical Detection of Earth's Coriolis Force?

• Geremia
In summary: Earth's rotation had an effect on the shells' trajectory, it would have been negligible.In summary, a beam of photons emitted from the north pole will follow the same trajectory as a beam of electrons emitted in the same direction assuming no atmosphere. However, a mathematical invalidation of this would also be interesting.
Geremia
Is there an experiment that uses photons or other particles to measure the effect of Earth's rotation on them? Thanks

Is that an indirect way to ask if photon experiences the Coriolis force?

Worded differently:

Suppose a beam of photons is emitted from the north pole, tangentially to the Earth's surface (so as to maximize a hypothetical Coriolis effect), will it follow the same trajectory as a beam of electrons emitted in the same direction (assuming no atmosphere)?

A mathematical (in)validation of this would also be interesting.

(hoping I'm not to far off your intended topic)

Laser ring interferometers can indeed measure the Earth's rotation.

i'm sorry, I'm a newbie here. could you explain how a laser ring interferometer actually work?

Dr Lots-o'watts said:
Is that an indirect way to ask if photon experiences the Coriolis force?
Not just photons but other particles, too, yes
Dr Lots-o'watts said:
Worded differently:

Suppose a beam of photons is emitted from the north pole, tangentially to the Earth's surface (so as to maximize a hypothetical Coriolis effect), will it follow the same trajectory as a beam of electrons emitted in the same direction (assuming no atmosphere)?

A mathematical (in)validation of this would also be interesting.

(hoping I'm not to far off your intended topic)
No, this is good.

Precision/correction to my earlier post : An initial direction that is tangential to the north pole maximizes our perception that the Coriolis effect accelerates things "towards the right". The Coriolis effect as such doesn't actually depend on latitude, only its lateral and radial components.

As for a mathematical proof that it doesn't affect a photon, it suffices to say that Fcoriolis as classically defined is proportional to the mass of the particle, which for a photon is zero, so Fcoriolis(photon) = 0, QED. If any corresponding effect can be calculated with GR, it is beyond my personnal scope.

As for ring lasers:

http://en.wikipedia.org/wiki/Sagnac_effect#Ring_lasers.

Dr Lots-o'watts said:
As for a mathematical proof that it doesn't affect a photon, it suffices to say that Fcoriolis as classically defined is proportional to the mass of the particle, which for a photon is zero, so Fcoriolis(photon) = 0, QED. If any corresponding effect can be calculated with GR, it is beyond my personnal scope.
This line of reasoning doesn't work. Remember, if something is massless then it doesn't require any force to accelerate it. I.e. by Newton's 2nd law a=f/m=0/0 which is undefined, not zero.

In fact, when a force is proportional to the mass what that implies is that the acceleration is independent of the mass, and it will therefore accelerate a massless particle exactly the same as a massive particle.

DaleSpam said:
This line of reasoning doesn't work. Remember, if something is massless then it doesn't require any force to accelerate it.
Okay, then let's work with, e.g., atoms of noble gases.

Geremia said:
Is there an experiment that uses photons or other particles to measure the effect of Earth's rotation on them? Thanks

As DaleSpam pointed out, there is purely optical equipment that measures the Earth's rotation: a ring laser interferometer measures the Earth's rotation with respect to inertial space.

However, the operating principle of ring laser interferometry is unrelated to Coriolis-type effects arising from the Earth's rotation.

Even in the case of ballistics detection of Earth rotation effects is difficult, if not impossible. During the flight through the atmosphere there are several air drag effects that will always swamp out any rotation of Earth effect. That is, in ballistics it is pointless to take rotation of Earth effects into account; you won't be able to tell the difference anyway.

Bullets travel too fast, the duration of the flight is too short. The deviation arising from Earth rotation effect is far smaller than the accuracy of the gun shot; any Earth rotation effect will be swamped.

You may have a chance with bolts fired with a high performance crossbow. I have read descriptions of indoor sessions where an incredibly tight grouping was achieved. Crossbow bolts may move slow enough to allow Earth rotation effects to be discernable.

Clearly, light and close-to-lightspeed particles move way, way too fast. I am convinced there is no chance at all of detecting Coriolis-type Earth rotation effects with light or close-to-lightspeed particles.

Cleonis said:
... in ballistics it is pointless to take rotation of Earth effects into account; you won't be able to tell the difference anyway.

Not so.

The Coriolis effects became important in external ballistics for calculating the trajectories of very long-range artillery shells. The most famous historical example was the Paris gun, used by the Germans during World War I to bombard Paris from a range of about 120 km (75 mi).

http://en.wikipedia.org/wiki/Coriolis_effect

dlgoff said:
The Coriolis effects became important in external ballistics for calculating the trajectories of very long-range artillery shells. The most famous historical example was the Paris gun, used by the Germans during World War I to bombard Paris from a range of about 120 km (75 mi).
http://en.wikipedia.org/wiki/Coriolis_effect

Yes, the Paris gun did exist, but it's aim was so terribly bad that it was useless for military offensive. It could only be used as psychological weapon, and that is what the Germans did. The shells could land anywhere in a five mile radius or so. None of the shells that was fired hit the city centre, they all landed in suburbs. But the fact that the gun could reach Paris was a terror factor of course.

The explosions were so violent that a lot of material was scraped from the inside of the barrel. The shells had to be fired in a precise sequence. Each next shell was a bit bigger, to compensate for the successive enlargement of the bore. After a dozen shots or so the barrel had to be transported back to the factory for resurfacing.

With other artillary it was possible to home in on a target. You fired a shot, you noted how far off you were, and then you applied corrections to elevation and direction. But the shots from the Paris gun just didn't repeat, so there was no point in trying to correct.

Bottom line: the story of the Paris gun being corrected for Earth rotation effect is a myth.

This talk about ballistics is off-topic. I am as much to blame, I mentioned ballistics when I wanted to illustrate that in all kinds of cases the Earth rotation effect is indiscernible.

Cleonis said:
This talk about ballistics is off-topic. I am as much to blame, I mentioned ballistics when I wanted to illustrate that in all kinds of cases the Earth rotation effect is indiscernible.
bolding by me.

Still wrong. The Earth's rotation indeed does effect a massive particles trajectory. And the OP now is asking about massive objects.

For small arms, the Coriolis effect is generally insignificant, but for ballistic projectiles with long flight times, such as extreme long-range rifle projectiles, artillery and intercontinental ballistic missiles, it is a significant factor in calculating the trajectory.

http://en.wikipedia.org/wiki/External_ballistics#Coriolis_drift"

Last edited by a moderator:
Last edited by a moderator:
dlgoff said:

The question of the original poster was whether experiments are conducted to find a Coriolis-type Earth rotation effect for light or for close-to-lightspeed particles.
I don't think such experiments exist, and I don't think any physicist considers such a setup.

External ballistics:
As far as I know in extreme long range rifling (range 1.5 kilometer) grouping within a radius of a meter or so can be achieved. With a nozzle velocity in the order of two or three times the speed of sound I estimate flight time will be a couple of seconds. That gives an Earth rotation effect in the order of 10 or 20 centimeter.
That's interesting. I suppose manufacturing precision has by now been pushed to a level where Earth rotation effect just comes into play.

I'm unfamiliar with modern artillary aiming capabilities. I only know that for WWI and WWII artillary Earth rotation effect was swamped by other factors affecting accuracy.

Last edited by a moderator:

## 1. What is the Coriolis force?

The Coriolis force is a phenomenon that occurs due to the Earth's rotation. It causes objects in motion on the Earth's surface to appear to veer to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

## 2. How is the Coriolis force detected optically?

The Coriolis force can be detected optically by using a laser beam and a rotating platform. As the platform rotates, the laser beam appears to curve due to the Coriolis force, which can be measured using a high-precision detector.

## 3. What is the significance of detecting the Coriolis force optically?

Optical detection of the Coriolis force allows for a non-intrusive and accurate measurement of the Earth's rotation. This information can be used in various fields such as meteorology, geology, and oceanography to better understand the Earth's dynamics.

## 4. How does the Earth's rotation affect the Coriolis force?

The Coriolis force is directly proportional to the Earth's rotation rate. As the Earth rotates faster near the equator and slower near the poles, the Coriolis force also varies in strength accordingly.

## 5. Can the Coriolis force be detected in other planets?

Yes, the Coriolis force can be detected in other planets with a rotating surface. However, the magnitude and direction of the force may differ from that on Earth depending on the planet's rotation rate and direction.

• Optics
Replies
7
Views
9K
• Introductory Physics Homework Help
Replies
2
Views
289
• Optics
Replies
0
Views
176
• Earth Sciences
Replies
32
Views
4K
• Introductory Physics Homework Help
Replies
13
Views
2K
• Optics
Replies
1
Views
2K
• Optics
Replies
1
Views
1K
• Astronomy and Astrophysics
Replies
4
Views
2K
• Introductory Physics Homework Help
Replies
5
Views
1K
• Classical Physics
Replies
9
Views
1K