# *BALANCED AND UNBALANCED FORCES

BALANCED AND UNBALANCED FORCES

• There are many different types of forces which act on objects.
• When Forces act in pairs but these are either balanced or unbalanced.

BALANCED FORCE

• Balanced forces do not cause change in motion (magnitude and direction of velocity/acceleration).
• They are equal in magnitude and opposite in direction.

UNBALANCED FORCE

• An unbalanced force always causes a change in motion. Causes change in magnitude and direction of velocity/acceleration
• When unbalanced forces act in opposite directions, there will be a net force

Net force

Magnitude: Vector difference between the two forces

Direction of the unbalanced force–Direction of the largest force

If forces are balanced the object doesn’t move.

FUNCTIONS OF THE UNBALANCED FORCE

If forces are unbalanced the object will do one of the following things:

Begins to move

Stop moving

Change direction

Speeds up

Decreases Speed

FUNCTIONS OF A FORCE

Make a body move

Accelerate a already moving object

Retard a already moving object

Stop motion

Change direction

Cause deformation

Remove deformation

Unbalancing of Rotors—–1

UNBALANCING

There is a net force acting on a system i.e. forces are not balanced.

CAUSES OF UNBALANCING

Unbalancing is caused by the followings:

• Eccentric rotating masses
• Eccentric reciprocating masses

Eccentricity causes the followings:

• additional stresses in the body and the material will fail at a lower load
• Causes unwanted vibrations

GRAPHICAL DEFINITION OF UNBALANCING

Unbalancing is due to non coinciding of mass axis (inertia axis) and axis of rotation. The perpendicular  distance between the two axes if parallel is eccentricity.

TYPES OF UNBALANCING

• Static Unbalance: Static unbalancing is due to mass axis (inertia axis) and axis of rotation do not coincide but these axes are parallel and are at some distance from each other.
• Couple unbalance: Couple unbalancing is due to mass axis (inertia axis) and axis of rotation do not coincide but these axes intersect at the center of gravity of the rotor
• Dynamic unbalance: Dynamic unbalancing is due to mass axis (inertia axis) and axis of rotation do not coincide but these axes intersect somewhere but not at the center of gravity of the rotor. Or these are neither parallel nor intersecting.

Dynamic unbalancing has the combined effect of static and couple unbalances.

SYMBOL USED FOR UNBALANCING—————U

MAGNITUDE OF UNBALANCING

U =m r                g mm

UNITS OF UNBALANCING——— g mm