Chapter 3 (A - 3.1 to 3.4) Moments of a force and Centre of Mass Flashcards
Moment of a force formula
Moment (Nm) = Force x Perpendicular distance from the point
What is a moment
The rotational (or turning) effect of a force
When does rotational equilibrium occur?
Sum of clockwise moments = sum of anticlockwise moments
What is the principle of moments
Sum of CW moments = sum of ACW moments
When is equilibrium reached?
When there is no resultant force or turning effect
Sum of clockwise moments about any point is equal to the sum of the anticlockwise moments around that point.
Unit of moment of force
Newton-metre (Nm)
What is another name for moments of a force
Torque
Conditions for equilibirum
Sum of forces applied on one side must be equal to the other/resultant force on body = 0
Principle of moments must apply
What is the centre of mass/gravity
A single point through which the object’s weight acts.
How to find the centre of mass of a plane lamina
Suspend the object, and a plumbline from the same point
Trace the thread of the plumbline with a pencil
Repeat using a different point
The intersection of the lines is the centre of mass
What are the 3 types of equilibrium
Stable
Unstable
Neutral
What is stable equilibrium
a state of equilibrium of a body such that when the body is slightly displaced it tends to return to its original position
What is unstable equilibrium
A state of equilibrium where the body is only balanced briefly. But the centre of mass can immediately pass the base
What is neutral equilibrium
even if the object is displaced, the centre of gravity always stays exactly over the point which is its base.
