*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 forces do not cause change in motion (magnitude and direction of velocity/acceleration).
- They are equal in magnitude and opposite in direction.
- 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
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
FUNCTIONS OF A FORCE
Make a body move
Accelerate a already moving object
Retard a already moving object
Unbalancing of Rotors—–1
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