Inertial frames of reference

  • Thread starter daveed
  • Start date
  • #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 cant 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, whats the modern view on this?
 

Answers and Replies

  • #2
Tide
Science Advisor
Homework Helper
3,089
0
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
Nylex
552
2
Newton's first law is true in inertial frames!
 
  • #4
daveed
138
0
then you cant say anything is a proper frame.

why wouldnt we be able to feel the earth's rotation?
 
  • #5
robphy
Science Advisor
Homework Helper
Insights Author
Gold Member
6,514
1,876
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
HallsofIvy
Science Advisor
Homework Helper
43,021
970
daveed said:
then you cant say anything is a proper frame.

why wouldnt 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.
 

Suggested for: Inertial frames of reference

  • Last Post
Replies
3
Views
372
  • Last Post
Replies
8
Views
1K
Replies
13
Views
624
Replies
15
Views
2K
Replies
12
Views
1K
  • Last Post
Replies
9
Views
278
Replies
17
Views
647
Replies
94
Views
3K
Top