M1 - Moments Confusion - Help Please? :)

Hello there,

Could someone please explain how to take moment, i know that its the distance multplied by the force, but when i go to answer a question i get stuck where to take moments from...

Could someone please help me? Thanks! :smile:

Reply 1

anameofsomesort

Its dependant on the situation, but probably a good idea to take moments from either the left or right far side of whatever situation you are analyzsing, that way you dont have moments on both sides which helps if you need to determine the force/s needed to make anticlockwise moments = clockwise moments.

Reply 2

apo1324

OP

11

How would i do this question:-

http://www.wjec.co.uk/uploads/papers/s08-980-01.pdf Q8 - Im soo confused.

Reply 3

recorta

At equilibrium, forces up (i.e. R forces at P&Q) equal forces down (i.e. the weight of the plank and any weights added to it).

In addition, equilibrium will not be maintained when the beam pivots (i.e. when the R force at either P or Q is 0 and the plank lifts up from that support).

First, draw out the model again with the weight on whichever side you fancy (personally, I'd go with the RHS because it's easier to think about it pivoting clockwise for some reason). Then think about what sorts of forces there will be when the plank starts to turn. Logically, where will the weight have to be? Then think about how to do the maths.

Reply 4

apo1324

OP

11

recorta

At equilibrium, forces up (i.e. R forces at P&Q) equal forces down (i.e. the weight of the plank and any weights added to it).

In addition, equilibrium will not be maintained when the beam pivots (i.e. when the R force at either P or Q is 0 and the plank lifts up from that support).

First, draw out the model again with the weight on whichever side you fancy (personally, I'd go with the RHS because it's easier to think about it pivoting clockwise for some reason). Then think about what sorts of forces there will be when the plank starts to turn. Logically, where will the weight have to be? Then think about how to do the maths.