Because these are two different issues:John Mcrain said:
Exactly. Using the CM is often practical because the acceleration of the CM is already fully described by the linear laws of motion (F = ma).Filip Larsen said:
A.T. said:
But you keep conflating the two issues, like you did in the old thread. The point was to clarify the difference, not to have the same confusion in two threads.John Mcrain said:
I already said that my IQ is to low to understand some physics abstraction,plus I struggle with english explanation.A.T. said:
To be frank, what I see in many of your posts/threads looks more like a stubbornness/lack of desire to learn than lack of ability to learn(among other issues). In order to learn, you first have to accept that what you currently believe is wrong, and you don't seem to want to do that. This particular issue is simple enough that pretty much anyone who can write a complete sentence should be able to understand it:John Mcrain said:
Object 2 rotate.russ_watters said:
Yes, even when you sit on one end, so that is the seesaw part at rest in your reference frame, your brain will still tell you that it's rotating around the axis in the middle.John Mcrain said:
Correct!John Mcrain said:
It isn't known if F1 and F2 are equal. You didn't explain why and you are bringing in axis of rotation when I explicitly told you not to. Explain why it rotates, and don't discuss axis of rotation.
Object 2 rotate because forces are not lie at same line...russ_watters said:
Yes but for design purpose you mast know that seesaw rotate about pivot point jont,otherwise you can weld joint and seesaw would not work ..A.T. said:
Close enough. The way I would word the answer it is that the object rotates because there is a net torque. Next question:John Mcrain said:
I say about point C if F1 and F2 is equal in magnitude...russ_watters said:
The correct answer is any point because of the prior answer: it rotates because there is a net torque. So, let's prove it.John Mcrain said:
Of course it rotates about the pivot point. What you are suggesting we are telling you here is exactly the opposite of what we are actually telling you.John Mcrain said:
russ_watters said:
You didn't need to assign a value to F and you used the wrong distance, but anyway, you got the same answer for each. There's a net torque about each point and it's the same torque.John Mcrain said:
russ_watters said:
A mechanical joint doesn't imply a unique rotation center. Look at segment between J and F the video below. Around which of its 3 joints (J, H, F) is it rotating?John Mcrain said:
Each interval is 1 unit of distance, so the torque about C is -1F + (-1F) = -2F (clockwise, by defining up and right as positive)John Mcrain said:
I count each square 1 unit..russ_watters said:
I told you what the distances were...John Mcrain said:
russ_watters said:
If you want to talk about an unique "center of rotation", you should define precisely (mathematically) what you mean by that. See this post for example:John Mcrain said:
Are you talking about yaw stability of an airplane?John Mcrain said:
Yes yaw stability for airplane,rocket..Lnewqban said:
For any reason, the airplane can yaw around its CG.John Mcrain said:
The center of gravity is a crucial factor in determining the yaw stability of an object. When the center of gravity is located ahead of the center of pressure, it creates a downward force that helps keep the object stable and prevents it from tipping over.
If the center of gravity is located behind the center of pressure, it can cause the object to become unstable and potentially tip over. This is especially important for objects that are moving, such as airplanes or cars, as an unstable center of gravity can lead to loss of control.
The center of gravity can be adjusted by changing the distribution of weight within an object. For example, in a car, moving heavy objects towards the front of the vehicle can help shift the center of gravity forward and improve yaw stability.
Yes, there are other factors that can affect yaw stability, such as the shape and size of the object, the speed and direction of movement, and external forces like wind or turbulence. However, the center of gravity is one of the most important factors in determining yaw stability.
One example is in airplane design. The center of gravity must be carefully calculated and placed ahead of the center of pressure to ensure safe and stable flight. Another example is in the design of tall buildings, where the center of gravity must be located within the base to prevent the building from toppling over.