The discussion centers on the principle of relativity and whether it is possible to determine if a ship, or bus, is moving. Participants argue that motion is relative, and experiments involving an insect or robotic fly inside a moving vehicle can indicate relative motion but not absolute motion. The consensus is that without an external reference point, one cannot definitively ascertain the movement of the bus or the fly. The conversation highlights the complexities of measuring motion and the importance of reference frames in understanding relativity.
PREREQUISITESStudents of physics, educators, and anyone interested in the fundamental concepts of motion and relativity will benefit from this discussion.
Or the fly was moving, and the bus was still.Meson080 said:If the fly crashes, then the bus is moving with uniform speed.
How does your remote determine if the fly is "still"?Meson080 said:I can know that it is still, because I have the remote.
Nick O said:How do you know that the bus is moving, and not the point with respect to which the fly is motionless? The bus might be perfectly still with the fly's reference point moving at a constant velocity.
Nick O said:What we are trying to say is that you can't know that the fly actually comes to rest. And if you could know, then it would be exactly as if you had a window to see whether external reference points were moving, because the fly would be synchronized with a known external reference.
Meson080 said:What happens if it synchronized?
Nick O said:Are you moving at the same velocity as the bus? If so, this tells you nothing. If not, then why do you need the fly?
Nugatory said:Right, your eyes will tell you whether it is the bus or the fly that is moving relative to you. But how do you know whether you are still or moving? How would you convince someone else who happens to be nearby, also watching the bus and the fly, but moving at the same speed relative to you as the bus, that it is him and the bus that is moving and not you and the fly?
Nick O said:Okay, what we need are scenarios. Tell me where these are wrong, and why.
Scenario 1: Bus moving at 100mph north.
The fly enters bus and comes to rest w.r.t. the bus. Therefore, the bus and fly are now moving 100mph north. The fly appears motionless, so you conclude that the bus is not moving.
Scenario 1: Bus motionless.
The fly enters bus and comes to rest w.r.t. the bus. Therefore, the bus and fly are now motionless. The fly appears motionless, so you conclude that the bus is not moving.
Meson080 said:The bus is drifting at uniform speed. I am performing the experiment in it by making the insect stay at a particular point inside the bus (but not physically in contact). What's the problem?
SteamKing said:How do you make the insect stay at a particular point inside the bus? It's not as easy as it seems.
Well, I guess all the world problems are solved then...Meson080 said:I am the one who has made the fly stand still using my remote.
Meson080 said:I can read the speed of the fly to be 0 towards north and it must stand still according to my remote controller.
My response to scenario 1 might help you.Meson080 said:If the fly crashes, then the bus is moving with uniform speed.A.T. said:Or the fly was moving, and the bus was still.
Meson080 said:I can read the speed of the fly to be 0 towards north and it must stand still according to my remote controller.
DrStupid said:That just postpones the problem. How does your remote controller know the speed of the fly?
Nick O said:So you and the remote are inside the bus, and you are flying a reference point from outside into the bus. That will indeed tell you whether or not the bus is moving with respect to the reference point, but it won't tell you which of the two is moving with respect to the earth.
You think that your bike speedometer will work, when the bike floats in vacuum?Meson080 said:How does the speedometer in your bike say your bike's speed?
A.T. said:You think that your bike speedometer will work, when the bike floats in vacuum?
How does your speedometer work?Meson080 said:But, my speedometer which says the speed of fly is surely going to work.
Meson080 said:How does the speedometer in your bike say your bike's speed?
A.T. said:How does your speedometer work?
If you cannot describe your proposed experiment, then there is nothing to discuss at all.Meson080 said:That's a technical thing. I am not discussing about it.
TheDemx27 said:Unless you are accelerating, you cannot tell whether the bus is at rest or not. At a uniform velocity, all of the forces are in equilibrium as they are when at rest. If they fly does fly into the car (perfectly) it will remain stationary with respect to the car as it is suspended within the air inside the car.
I often thought about this situation as well, anecdotally.
A.T. said:If you cannot describe your proposed experiment, then there is nothing to discuss at all.
How?Meson080 said:I think it is possible.
DrStupid said:It counts the revolution of the wheel relative to the bike and measures the corresponding time. Together with the radius of the wheel this gives the tangential speed of the tire relative to the bike. As long as the bike is rolling on the ground without slip, the result is equal to the speed of the ground relative to the bike and to the speed of the bike relative to the ground respectively. In short: the speedometer measures the speed of the bike relative to the ground.
How does your remote control measures the speed of the fly - especially relative to which reference?
If your speedometer works, why don't you attach it to the bus directly, to know if the bus is moving? Why do you need a robotic fly with a remote control?Meson080 said:I just wanted to say that, as your speedometer works, even my speedometer works.
It is the key part of your experiment, that you have to define precisely. If you cannot define your proposed experiment, then there is nothing to discuss at all.Meson080 said:Its a technical aspect.
A.T. said:How?
Meson080 said:Remember I am considering vaccum.