chapter 5 turning effect of forces Flashcards
moment of a force
product of a force (F) and the perpendicular distance from the pivot (d) to the line of action of the force
Moment = F x d
POM
when a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot
Mclockwise = Manticlockwise
RF = 0
centre of gravity
the point through which its whole weight appears to act
(line of action of weight is always 90 degrees down)
stability
ability of an object to return to its original position after it is slightly displaced
stable equilibrium
- object slightly toppled to right
- line of action of weight still lies within the object’s base area
- weight creates anticlockwise (to the left) moment about point of contact
- block returns to original position
unstable equilibrium
scenario 1
- object toppled to the right until line of action of weight passes through/directly on point of contact
- no perpendicular distance from pivot (point of contact) and line of action
- no (anticlockwise) moment produced about pivot
- object about to topple
unstable equilibrium
scenario 2
- object toppled to the right until line of action of weight is outside of base area
- (line of action is on the right of the pivot) creates clockwise moment about point of contact
- block topples
neutral equilibrium
eg block is lying on its biggest flat side
1. block is slightly displaced, line of action of weight remains at same height
2. line of action of weight and contact force of block on surface meet at same point
3. moment of weight about contact point is 0
4. object stays in position to which it is displaced
what affects stability of object?
- centre of gravity of object: lower the CG, more stable (lower CG by increasing mass of object at bottom eg a double decker bus has more passengers at bottom than top!)
- base area: wider the base area, more stable
