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Tendency of Force to Rotate a Body
Two effects of force: 1) Move a body in the direction of its application2) Rotate a body around an axis.
Moment Arm
M Fd
Tendency of the force to rotate a bodyIs proportional to
F and d
d: perpendicular distance from the axis to the line of force action
Right-Hand Rule
Moment in the direction of thumb
Fingers curl in the direction of the tendency to rotate
Many-Particle Interactions
1
2f21
f13
3
f12
f31
f23
f32
F3
F1
ii
F 0
For an N particles system, in equilibrium
Many-Particle Interactions
i ijj i
F f 0 1,2,i
i i i iji i j i
r F r f 0
i i i ijj i
r F r f 0
For an N particles system, in equilibrium
Can you prove: i iji j i
r f 0 ?
i ii
r F 0Therefore:
Need Newton’s 3rd law
Newton’s 1st law:
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