## Azteck 2 years ago Can a passenger in a closed carriage of a train travelling at constant velocity across a very smooth section of the Nullarbor Plain demonstrate or measure that they are moving relative to the ground? Could they measure a change in velocity [ie. acceleration] from within that frame of reference?

1. Mashy

why don't you think about it... the entire earth is moving around the sun in a circular motion.. but the circle is so big.. that we can think of it as almost a straight line motion with constant speed.. now you tell.. is it possible for you to make out .. that earth is moving??

2. Azteck

No...but for the second part of that question, is it yes?

3. Mashy

imagine when you are in bus.. why do you think you are able to make out the motion???..

4. Mashy

sealed air tight bus.. so no air from outside hits your face :P

5. Azteck

SO basically what are you saying about the second part of the question? Could you determine the acceleration of the train in that frame of reference?

6. Mashy

well.. i want you to think.. when you are inside a bus... can you or can you not make out whether you are moving or not?

7. Azteck

Yes of course.

8. Mashy

can you tell me.. when is it that it becomes the most obvious to you tat you are moving??

9. Mashy

maybe when you take a sharp turn.. or maybe sudden brakes.. thats when its really really obvious right?

10. Azteck

Yes.

11. Azteck

But when you're accelerating, you can still feel that sudden push/urge.

12. Azteck

Is what I just said correct?

13. Mashy

yes.. so when you are accelerating.. you get that pseudo force we call it as an inertial force.. during a right turn you tend to go towards left..(centrifugal force ).. and hence you can make out motion!.. so acceleration can be made out within the frame of referrence

14. Azteck

frame of reference, which is relative to the ground? Okay thanks for your help mate. Appreciate it.

15. Mashy

yes.. relative to ground.. :)..

16. Mashy

when you are in uniform motion, if you look at the ground.. you dunno whether the ground is going back or you are moving forward.. infact both are right.. thats where Eisntien talked about relative motion.. he said that motion is only a relative term.. but when we talk about accelerated motions.. its no longer relative.. cause you feel the inertial force..

17. Azteck

Ah I see. This all makes sense. Everything's come together in my brain. Thank you very much @Mashy. Cheers.

18. Mashy

lol.. no problem ;-)