Why don't we feel the Earth's rotation?

In summary, the laws of classical mechanics hold true with Earth as a frame of reference due to the Earth's constant rotation, which causes non-inertial effects that are small on a human scale but noticeable on a larger scale. This is known as the Coriolis effect and is responsible for phenomena such as the rotation of storm systems. However, in order to accurately account for these effects, they must be taken into consideration in certain situations, such as long-range artillery fire.
  • #1
CrazyNeutrino
100
0
Pardon me if this seems like an incredibly naive question. Perhaps the question could also be rephrased as such: "Why do the laws of classical mechanics hold true with Earth as a frame of reference?"

A quick google search turned up the usual answer: the Earth rotates at a constant speed. Regardless of what speed the Earth is rotating at doesn't the fact that it is rotating/changing velocity mean that objects on the surface of the Earth are constantly accelerating? If so then why don't we feel the Earth's rotation and why is Newton's second law valid? Isn't it no longer an inertial frame of reference if the Earth is accelerating.
 
Physics news on Phys.org
  • #2
You don't notice it because the non-inertial effects are very small on an "across the room" kind of scale. But go up in scale and you will notice that the Earth's surface frame isn't inertial. You may wish to look up the Coriolis effect - a non-inertial-frame effect, the standard example of which is the way storm systems rotate.
 
  • #3
Ibix said:
You don't notice it because the non-inertial effects are very small on an "across the room" kind of scale. But go up in scale and you will notice that the Earth's surface frame isn't inertial. You may wish to look up the Coriolis effect - a non-inertial-frame effect, the standard example of which is the way storm systems rotate.
So are Newtons laws an approximation on earth?
 
  • #4
In the frame attached to the Earth's surface, yes. It's a rotating frame. I gather that long range artillery fire will miss if you don't account for that fact, and I've already mentioned the weather. But you'll need to be an extremely careful experimentalist to spot the errors in the lab.

That said, you can always pick an inertial frame and work in that; Newton's laws will be exact (up to relativistic corrections, anyway). But the Earth's surface is not stationary in such a frame.

Edit: Actually, I think it depends what you mean by Newton's Laws. In some senses they apply in any frame; they just don't take the familiar simple form in a non-inertial frame. You'll still find that momentum and energy are conserved and things like that. It's just that what you (in your rotating frame) are calling a straight line is not what an inertial frame calls a straight line. Inertial forces (like the Coriolis force) drop out of the maths to explain why things don't follow what you want to call a straight line.

Edit 2: xkcd: https://xkcd.com/123/
 
Last edited:
  • Like
Likes russ_watters
  • #5
CrazyNeutrino said:
f so then why don't we feel the Earth's rotation and why is Newton's second law valid?
Sufficiently sensitive experiments do feel the Earth's rotation. Our inner ear and other proprioceptive organs are just not sensitive enough.
 
  • #6
CrazyNeutrino said:
A quick google search turned up the usual answer: the Earth rotates at a constant speed. Regardless of what speed the Earth is rotating at doesn't the fact that it is rotating/changing velocity mean that objects on the surface of the Earth are constantly accelerating? If so then why don't we feel the Earth's rotation and why is Newton's second law valid? Isn't it no longer an inertial frame of reference if the Earth is accelerating.

Perhaps I misunderstand but..

Accurate weighing scales have to be calibrated according to the latitude where they will be used. As I recall the apparent weigh of an object is 0.3% less at the equator due to the Earth's rotation. Not enough for us to feel it.

There is also this effect if you are moving but the variation is even less significant..
https://en.wikipedia.org/wiki/Eötvös_effect
 
  • #7
Ibix said:
I gather that long range artillery fire will miss if you don't account for that fact

Absolutely. I recently saw an old manual on the targeting of battleship cannons and they had to take the Earth's rotation into account in order to accurately fire at long ranges. When your shell has a flight time of around a minute and a half and goes around 20 miles, you start to approach the scale at which the Earth's rotation has an appreciable effect.
 
  • #8
Drakkith said:
Absolutely. I recently saw an old manual on the targeting of battleship cannons and they had to take the Earth's rotation into account in order to accurately fire at long ranges. When your shell has a flight time of around a minute and a half and goes around 20 miles, you start to approach the scale at which the Earth's rotation has an appreciable effect.
Are you thinking of this thread? https://www.physicsforums.com/threads/coriolis-effect-on-ballistics-and-old-chart.917776/
 

1. Why don't we feel the Earth's rotation?

We don't feel the Earth's rotation because of its constant speed and the lack of any external forces acting on us to change our position. Additionally, we are also rotating along with the Earth, so our bodies are not experiencing any relative motion.

2. If the Earth is rotating, why don't we feel dizzy or disoriented?

The Earth's rotation is a gradual, smooth movement that our bodies have adapted to over time. This, along with other sensory cues such as our visual and vestibular systems, help us maintain balance and a sense of orientation.

3. Can we ever feel the Earth's rotation?

Yes, we can feel the Earth's rotation indirectly through the effects of its rotation, such as the Coriolis effect which influences the direction of moving objects on the Earth's surface. However, we do not directly feel the Earth's rotation itself.

4. Why is the Earth's rotation important?

The Earth's rotation is important for many reasons. It is what causes day and night, influences the Earth's climate and weather patterns, and helps regulate the Earth's magnetic field. The rotation also plays a role in shaping the Earth's topography and the distribution of land and water on its surface.

5. Can the Earth's rotation change?

Yes, the Earth's rotation can change over long periods of time due to factors such as the gravitational pull of other celestial bodies and changes in the Earth's mass distribution. However, these changes are very gradual and not noticeable to humans in our lifetime.

Similar threads

Replies
8
Views
2K
Replies
2
Views
686
Replies
4
Views
2K
Replies
5
Views
706
Replies
5
Views
1K
Replies
13
Views
3K
Replies
10
Views
3K
Replies
7
Views
2K
Replies
7
Views
2K
Back
Top