Biomechanics Questions

Equivalent force systems

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2 years 5 months ago #250 by Ahmed Abdul-Aziz
I did not understand the direction of the moment of the force at the red point in the equivalent force systems in webinar 5. I would be grateful if more explanation is provided.
Thanks
:) :)

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2 years 5 months ago #255 by Giorgio_Fiorelli
Please give me the time of the webinar, so I can check it more quickly

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2 years 5 months ago #256 by Ahmed Abdul-Aziz
Thanks Prof!!!!!

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2 years 5 months ago #257 by Ahmed Abdul-Aziz
The time is 13 min 15 sec.

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2 years 5 months ago #259 by Giorgio_Fiorelli

It is really hard for me to explain better than in the video, but I will try.

The force of 100g is not applied to the red point, but 5mm away from it.
The effect of the force alone on the red point is therefore:
one Force of 100g AND one Moment of 500gmm (100*5).
The direction of this moment is clockwise (think of the spin given by the force to the wheel hinged on the red point).

BUT, on the white point, we have also a Moment of 500 gmm counter-clockwise. This moment has the same effect everywhere (go back to see the characteristic of the couple), including the red point.

Therefore, on the Red point we have:
1) the force of 100g
2) the moment produced by the force applied at the white point. 500gmm CW
3) the effect of the couple applied at the white point: 500gmm CCW

SINCE THE TWO MOMENTS ARE EQUAL IN MAGNITUDE AND OPPOSITE IN DIRECTION
THEIR SUM IS ZERO. THEREFORE AT THE RED POINT, WE HAVE A FORCE AND NO MOMENT.
IF THE RED POINT IS THE CENTER OF (MASS, GRAVITY, OR RESISTANCE) THE OBJECT WOULD TRANSLATE.
The following user(s) said Thank You: Ahmed Abdul-Aziz

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