Is it possible to tell whether ship is moving or not?

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Discussion Overview

The discussion revolves around the concept of motion and whether it is possible to determine if a ship (or bus) is moving without external reference points. Participants explore the implications of the principle of relativity, particularly in relation to mechanical experiments and relative motion, while considering hypothetical scenarios involving insects and robotic models inside a moving vehicle.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that mechanical experiments can reveal whether a system is moving, using examples like an insect or robotic model inside a bus.
  • Others argue that the observations made by an insect or robotic fly do not definitively indicate the bus's motion, as motion is relative to the observer.
  • A participant suggests that if a fly is stationary relative to the bus, it will not be hit by the bus even if the bus is moving at a uniform speed.
  • There is a discussion about differential acceleration and its effects, with some participants seeking clarification on the term.
  • A later reply questions the existence of an "absolute velocity" that could be measured without a reference frame, proposing that relativistic effects might provide insights into such a measurement.

Areas of Agreement / Disagreement

Participants express multiple competing views on the nature of motion and relativity, with no consensus reached regarding the possibility of determining absolute motion or the implications of their thought experiments.

Contextual Notes

Limitations include the dependence on definitions of motion and the unresolved nature of whether absolute velocity can be measured without reference to other objects.

  • #61
Meson080 said:
It is just my idea that it is possible.
So you have actually no idea how to determine whether something is moving or not. You just have the idea that it is possible.
 
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  • #62
@A.T: Yes I just have the idea that it is possible. What's the problem?
 
  • #63
Meson080 said:
Yes I just have the idea that it is possible.
Great. When you have figured out how, let us know.
 
  • #64
A.T. said:
Great. When you have figured out how, let us know.

Sorry, I have already said that unless you say anything why it is important to speak about technical part and mainly why you think it is "impossible" to create such a device, I can't say anything (to stay on topic and be according to forum rules). Thank you for your support until now. Good night.:zzz:
 
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  • #65
Meson080 said:
Sorry, I have already said that unless you say anything why it is important to speak about technical part and mainly why you think it is "impossible" to create such a device, I can't say anything (to stay on topic and be according to forum rules). Thank you for your support until now.

It is important because all speedometers operate by measuring the speed of something relative to something else.

For example:
- The speedometer in a car counts revolutions of the wheels in a given time, multiplies by the know circumference of the wheel, and uses that to calculate the speed of the car relative to the road; the speedometer will produce an incorrect speed value if you lock the wheels so that the rotation of the wheel is no longer related to the speed of the car.
- A GPS measures the movement of the receiver relative to satellites orbiting the earth; because we know where the satellites are relative to the Earth it can calculate the its speed relative to the earth.
- Radar systems measure the speed of aircraft relative to the source of the radar transmitter and receiver.
- When we speak of the speed of the Earth in its orbit around the sun (several kilometers a second) we are measuring its speed relative to the sun.
 
  • #66
The problem is that velocity is always measured with respect to something else. There are a few ways to build speedometers that work in vacuums, such as an accelerometer with an integrator, radar, GPS, or such like.

However, each of these is with respect to a reference velocity. If you use the radar method, then the reference is the velocity of the transmitter, which is an unknown factor. If you use an accelerometer, then the reference velocity is the initial velocity, which is unknown. GPS can be faulty if, for example, the satellites are struck by meteors and put in an unknown orbit.
 
  • #67
Enough.

Meson080, it is impossible because the laws of mechanics are second-order differential equations. In other words, they contain acceleration, not velocity.

Thread closed.
 
Last edited:

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