BR physics chapter 4 ex 4.2b

[2010premed]

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WHy is it that as one mass moves closer to the fulcrum, the other ust also move closer to the fulcrum to keep things balanced?

 

[Rayhaan]

Think of a seesaw. If I'm at one end and you are at the other. If only I shuffle inwards we lose balance. But if you move with me towards the fulcrum, then we balance it out!

 

[fizzgig]

the 'moment' is the tendency to rotate that a force on an object creates. it is equal to force*distance. push at an object's center of mass, distance is zero, no tendency to rotate if the object isn't pinned anywhere.

for a see saw to be still, the sum of the moments have to equal zero. the see saws weight is at the center of mass, and if the fulcrum is there too, the weight contributes no moment. so the applied forces on either side decide.

force1*distance1 = force2*distance2