Inertial frames of reference

In summary, determining if something is a proper inertial frame of reference involves looking at whether or not it is accelerating. While we may not be able to physically feel the Earth's rotation, it is still a form of acceleration and therefore not an inertial frame. The modern view, based on the general theory of relativity, states that acceleration and forces are indistinguishable. Therefore, we cannot use our physical sensations to determine if we are in a proper frame of reference. Techniques such as using an accelerometer or a Foucault Pendulum can be used to detect rotation and acceleration. Ultimately, it is not possible to definitively say if something is a proper frame of reference.
  • #1
daveed
138
0
how do you determine if something is a proper inertial frame of reference? the Earth is but a car isnt? you can feel a car accelerate, even though you are in it, but you can't feel the Earth accelerate as it changes directions in its orbit.. is there a poitn after which you don't feel accelerations much? but this is just Newtonion, what's the modern view on this?
 
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  • #2
An inertial frame of reference is one that is not accelerating. Just because you can't feel it doesn't mean it's not accelerating. Sitting here on the surface of the Earth we are NOT in an inertial frame since the planet is rotating and we're rotating right along with it (rotation is a form of acceleration!).
 
  • #3
Newton's first law is true in inertial frames!
 
  • #4
then you can't say anything is a proper frame.

why wouldn't we be able to feel the Earth's rotation?
 
  • #5
Use an accelerometer... a cube containing a mass supported by springs. If the mass is centered, then its "reference frame" is not accelerating. To detect rotation, you might need an array of accelerometers.

(A Foucault Pendulum can detect rotation.)
 
  • #6
daveed said:
then you can't say anything is a proper frame.

why wouldn't we be able to feel the Earth's rotation?

True. In a sense, the general theory of relativity is based on the concept that you can't (locally) distinguish between a force and an acceleration.

The Earth's rotation has the effect of making you a little lighter than you would be if the Earth were not rotating. You don't "feel" the Earth's rotation for two reasons: First, it is with you all the time so you have nothing to compare it to. Second, if you were to go from the north or south pole to the equator, you would become slightly lighter but the effect would probably be too small to measure.
 

What is an inertial frame of reference?

An inertial frame of reference is a frame of reference in which Newton's first law of motion holds true. This means that an object at rest will remain at rest, and an object in motion will continue to move at a constant velocity, unless acted upon by an external force.

What is the difference between an inertial frame of reference and a non-inertial frame of reference?

An inertial frame of reference is a frame of reference in which Newton's laws of motion hold true, while a non-inertial frame of reference is a frame of reference in which these laws do not hold true due to the presence of non-inertial forces, such as acceleration or rotation.

What is the significance of inertial frames of reference in physics?

Inertial frames of reference are important in physics because they provide a consistent and reliable way to measure and describe the motion of objects. They also allow for the application of Newton's laws of motion, which form the basis of classical mechanics.

How do we determine if a frame of reference is inertial?

A frame of reference is considered inertial if an object at rest in that frame will remain at rest and an object in motion will continue to move at a constant velocity, unless acted upon by an external force. This can be tested by observing the motion of objects in the frame and checking if Newton's first law of motion holds true.

Can an object be in both an inertial and non-inertial frame of reference at the same time?

No, an object can only be in one frame of reference at a time. However, an observer can be in a non-inertial frame of reference while observing an object in an inertial frame of reference. This can lead to apparent violations of Newton's laws due to the effects of non-inertial forces on the observer's perception.

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