Turning Efffect of Forces

3 Cases of Equilibrium

Case #1: (Stable equilibrium)

Stable equilibrium is due to it returning to
its original position without toppling

Things to note

Its Centre of gravity rises and then falls back again! :D

The line of action of its weight lies inside the base area of
the cone

The anti-clockwise moton of its weight is about the point of contact(at the side of the cone) causes the cone to return to its original position! :D

Case #2: (Unstable equilibrium)

Unstable equilibrium because if it is tilted slightly, it topples over :(

Things to note

Its centre of gravity falls and continues to fall further

The line of action of its weight lies outside the base area of the cone

The clockwise motion of its weight about the point of contact(tip of the cone, upside down)

Case #3: (Neutral equilibrium)

Neutral equilibrium because if it is sloghtly displaced or rolled, it will stay in its new position

Things to note

Its centre of gravity neither rises nor falls; it remains at the same level about the surface supporting it

THe lines of action of the force of weight and contact always coincides

There is no moment provided by its weight about the point of contact to turn the paper cone

CONCLUSION

Centre of gravity is as low as possible

The area of its base is as wide as possible

Definition

Stability refers to the ability of an object
to return to its original position after it
has been tilted slightly

the moment of the force is the turning effect of a force about a point or the ability of a force to make something turn.

the moment of a force is also called the torque

the turning effect/moment or a force depends on
1.magnitude of the force
2.perpendicular distance between the points of application of the force and pivot.

How does a beam balance
measure mass?

Weight=mg
Where g is the gravitational field strength or acceleration of free fall.
Similarly, the force acting on the total standard masses is Sg

Moment aout a pivot is "F x d"
Thus, anticlockwise moment = mg x d
and clockwise moment = Sg x d

For the beam to balance, the turning effects of these two forces must be equal. Therefore,
mg x d = Sg x d
Simplifying, m = S

Thus when the equal-arm beam is balanced (or in equilibrium), the mass of the object m is equal to the total standard masses S.

What is "Principle of Moments"

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

Conditions for equilibrium

When an object is in euilibrium, it must satisfy both
conditions as follows,
1. All forces acting on it are balanced, i.e. resultant force is zero
2. The resultant moment about the pivot is zero, i.e. the Principle of Moments must apply.

Why does a uniform metre rule
balance only at the 50cm mark?

Because that is the point where the whole weight of the body seems to act.

What is centre of gravity?

Is the point where the whole weight of the body seems to act

How to find the centre of gravity

For a regular-shaped object the centre of gravity is at its centre (or geometrical centre)
For an irregular object its centre of gravity is always vertically below the pivot when it is hanging freely about it