- #36
david smith
- 26
- 0
DaleSpam said:OK, I can appreciate that.
So, aside from the trivial algebraic manipulation of the equation, the only actual conceptual change of the D'Alembert approach is to consider inertia (-ma) to be a force. This is equivalent to working in the non-inertial rest frame of the object under consideration. In this frame there exists a ficticious force equal to -ma that must be introduced in order to have Newton's first and second laws hold.
Are you familiar with the concepts of non-inertial reference frames (e.g. rotating reference frame) and ficticious forces (e.g. centrifugal force)? If not, then I would recommend you begin studying those topics in order to understand the concepts in the D'Alembert approach.
The inertial force is like any other ficticious force. In particular it violates Newton's 3rd law and it is always proportional to the mass of the object. Ficticious forces can do work in the non-inertial coordinate system and accelerometers cannot detect acceleration due to ficticious forces.
Dale
I had learned about centrifugal / centripedal and coriolis force/effect but I did some reading to refresh and very useful it was too.
However at the end of the day centrifugal and coriolis forces are effects of perception due to the observers viewpoint being within the inertial rest frame or the rotating frame.
They are not forces at all as can be acertained by the observer outside the rotating frame who see that it is the rotating frame that chages direction and experiences acceleration, whereas the particle within it continues unhindered in the same direction.IE Newtons first law.
The centrifugal force feel as if it is at 90dgs to the centre of rotation beacuse the inside viewers perception of the acceleration changes at the same angular velocity as the objects.
Centripedal is a real force reaction to centrifugal force and it appears to me that Inertial force is a real reative force to acceleration.
So I read this paper, On the Origin of Inertial Force, C. Johan Masreliez Redmond, WA
jmasreliez@estfound.org. Which gives a very thorough explanation of the origin of inertial force, much of which was beyond me but essentially he is saying inertial force is a reation to acceleration within the inertial reference frame. IE unlike gravity and almost opposite to gravity it cannot be felt at rest whereas gravity cannot be felt in freefall.
So as such if a body requires a force to accelerate it then there are two questions.
You can't apply a force without an opposing force. So if a body with momentum collides with another body at rest, the body at rest has to accelerate and invoke a reactive inertial force. However the first body cannot apply any force to accelerate the second body until the second body has accelerated so then how can the applied force accelerate it. This appears to be a chicken and egg situation.
And
If two bodies act on each other in the way explained above then there are two inertial forces. One with a negative acceleration and one with a positive acceleration repectively related to their mass. With the other ficticious forces there was no acceleration and no change of direction IE no force.However with this configuration there are two ficticious forces that do cause acceleration and change of direction. Therefore they cannot be ficticious. Can they?
Obviously I still can't see inertial force from your perspective even tho I understand what you are saying. F=ma but ma is not an opossing force like a = f/m gives an equivalent sum but is not equal to a. Is this because you always view from the perspective of acceleration and I from the perspective of force. Therefore I always see balanced forces and you see unbalanced forces.
Ayway I've done many hours of reading and you have helped me to understand more, so its all good.
Cheers Dave
Last edited: