FORCE, MOMENT AND BALANCE

ByM. Firdaus, MT

www.dauspoli.co.cc

FORCE

• Interaction of objects

• Force can cause :– The speed of the object changes– Operating on objects– Deforming objects

Force Ilustration

Force F acting on the body that moves with constant speed s as far as giving rise in the

amount of W = F.s

Objects that have elastic strain (extension) due to forces acting

Schematic relationship of the mechanical force

Newton’s Law :“Any object at rest will remain silent and any

moving objects will keep moving straight uniformly, unless there is an unbalanced external force that forces the object to change the situation”

Or in the form of equations expressed :

Where : F = force resultant

0F

TORQUE

• Moment of force is a force to the point by multiplication of force by the arm of force

• Mathematically expressed as follows :

= F x d

Where : = Force (N) d = arm of force (m) M = momen of force (N.m)

An illustrative example

COUPLE MOMENT• Couple is a pair of two parallel forces, equal and opposite. Effect of

coupling on a body is to allow the object rotates. The amount of coupling is expressed in the moment of coupling

• The moment of coupling is the multiplication of force by the distance between these two forces. Mathematically :

Where : M = couple moment (N.m) F = force (N) d = distance between of two force (m)

dFM .

An illustrative example

Moment coupling that works towards the point O :

M = 2 (1,5) = 3 N.m

PARTICLE BALANCE

• Particles are objects with no size and is treated as a point, so that rotation and vibration can be neglected in advance

• The particle is said to be in balance if eligible :

“total force acting on the particle equal to zero”

Or in equation : F = 0

RIGID BODY BALANCE

• Rigid body (rigid bodies) is an object that will not deform (change shape) when a force acts on it

• In actually condition, a real object will change shape when receiving the force in the certain limit

• Rigid body is said to be in balance if it met two conditions :1. The number of forces acting on rigid body is

equal to zero, in equation :

2. The number of moments about any point equals zero,in equation :

0F

0M

CENTER OF MASS

• Center of mass is a point where the mass of the object or particle system centered

• the external forces acting on the body or particle systems work at that point

• If the object or particle system is in motion, the motion of center of mass can be considered a particle motion

An illustrative example

Force dynamic application