Re: Physical wavelength vs relative wavelength


"Greg Neill" <gneillREM@xxxxxxxxxxxxxxxxxx> wrote in message
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"Spaceman" <Realspace@xxxxxxxxxxx> wrote in message
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"Greg Neill" <gneillREM@xxxxxxxxxxxxxxxxxx> wrote in message
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Equal masses makes things simpler. Assuming an elastic
collision (like two billiard balls hitting head on),
since you've specified the relative speed of 100mph,
the center of momentum frame will have an origin situated
exactly halfway between each body with them approaching the
origin at 50 mph each. After collision they will rebound
at 50 mph each in that frame.

We don't know the speed,
all we know is the relative speeds to each other..
so it could have been 25mph and 75 mph,
or 10mph to 90 mph
or even 0 mph to 100mph..

I specified the center of momentum frame. In that
frame the speeds of the two equal mass objects is
the same. Note that this is not the same frame as
the observer; it's a frame used to simplify the
analysis.

Ok,
so you picked a frame but you don't know where it is
actually yet.


so, you can't say anything about the objects speeds
before the collision until after the collision occurs.

You can in the center of momentum frame.

The center of momentum that you don't know where
you are yet..
OK



I asked you how would you find what the speed actually was.
I also did not make the objects inelastic.
Why do you change the problem?
Let's say we have 2 donuts doing such.

If you want a specific answer you must specify specific
conditions. A collision can be perfectly elastic (no
KE lost in collision), perfectly inelastic (the bodies
stick together after collision) or somewhere in between.
In the somewhere in between case, at least specify the
coefficient of restitution of the colliding bodies.

Donuts make it very easy,
I can't believe you can figure such out.
:)



:)


The observer can pin down the center of momentum frame with
an actual measurement of one of the velocities (either
object, before or after collision) from his own point of
view.

How can his point of view have a "rest" frame to know he
is not in motion also?

The observer is always at rest in his own frame of
reference.

(you are going to have to use Earth as a rest frame for him huh?)

No, the observer's frame is fine no matter what his
state of motion, provided it's inertial.

Ok,
you still can not grasp anything about the speeds
except they are traveling towards each other at 100mph.



LOL
(both objects before collision only show a 100 mph
towards each other speed) (that is the most the observer
can find out also, if using his own relative frame)
You can not get any other info from that until
after the crash.

So,..
We have no data before the collision except the objects
have a relative speed towards each other of 100 mph
so all we truly can know before the collision was
they will collide at 100mph.
remove the elastic conditions.
use donuts.
how do you find what donut was doing what speed?
We would need to examine the aftermath correct?

Yes, if no other prior information is given.

That is all we have.

How do you know what donut was doing what speed?
And why do you need velocity?
You forgot how to use basic speeds of objects?

You need at least one velocity in order to determine the
motion of the center of momentum frame with respect to
the observer.

If you do,
than that is a bad way to determine what speeds
the dunuts were doing.
Examining the after math of a donut collision
can easily find the seperate relative speeds of the donuts.
compared to their crash site.
I think it is funny you do not know how to do such.
:)



.

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