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MrAl said:The abs signal is trying to move the coil back and forth rapidly, and if the coil had zero mass it would actually move from zero to maximum and back again as the abs(sin(wt)) kept changing.
steveB said:There is also the damping effect which is discussed.
And Steve mentioned square law effect
In the "another document" it is said that no core is used for moving coil in an electrodynamometer so that there are no hysteresis and eddy current losses.
PG,
You may find this document helpful.
https://www.electro-tech-online.com/custompdfs/2012/10/14188_ch3.pdf
I have a question for MrAl also. You mentioned the torque being an averaging of abs(sin), but I wonder if it is actually an averaging of sin^2 since the meter seems to be a square law effect. I haven't taken the time to analyze this in detail yet, but I figured I'd run this thought by you first, before spending time on it.
If true, the squaring will double the frequency and make the averaging effect even better. There is also the damping effect which is discussed. Hence, not only is the mass unwilling to move at high frequency, but it seems there should be higher electromagnetic damping for any high frequency or fast movement.
... the friction stays the same ...
when the force (or, rocket's thrust) changes from "O" to "A", it takes the trolley 10x distance toward right of the screen.
steveB said:For sinusoidal variations, speed is proportional to frequency and it is also proportional to displacement amplitude.
steveB said:How far can a big heavy mass move when the force goes from 0 to A at a very high frequency. Before the mass has moved a tiny amount, the force is already cycling back to the negative side of the cycle.
Are you referring this formula, v=ω*r*cos(ωt), for simple harmonic motion?
Okay. When the rocket is turned on, the trolley moves toward right and stays there afterwards. Let's say the trolley 2 feet. Could you please explain how things will go on between "O" --> "A" --> "B"? Why would the trolley move a distance of 2 feet in the first place?
In steady state, the position will vary sinusoidally as [latex]x(t)=X_{DC}+X_0\cdot \cos \omega t[/latex]
...
The 2 feet distance is the DC part of the solution, as described above. There is an average force from the rocket that must be counterbalanced by the average spring force. The DC component has no friction force since friction is proportional to frequency and frequency is zero for the DC part of the solution....