• FIRST CONDITION OF EQUILIBRIUMFIRST CONDITION OF EQUILIBRIUM• STATIC AND DYNAMIC EQUILIBRIUM STATIC AND DYNAMIC EQUILIBRIUM • KINDS OF FORCESKINDS OF FORCES• FREE-BODY DIAGRAMS FREE-BODY DIAGRAMS • SUGGESTED STEPS IN SOLVING PROBLEMSSUGGESTED STEPS IN SOLVING PROBLEMS

NEWTON’S LAWS OF MOTION

NEWTON’S LAWS OF MOTION

NEWTON’S FIRST LAW An object sitting at rest will remain at rest if the sum of all forces acting on the object is zero. Similarly, if an object is moving and the sum of the forces acting on the object is zero, then the object will continue to move in the same direction with same speed, therefore, in Equilibrium.

ΣF = 0

First Condition of EquilibriumThe body or system at this condition remains at rest or moves in a straight line with constant velocity. (Translational Equilibrium)Types:

a)Static Equilibrium – refers to all objects or systems at rest

b)Dynamic Equilibrium - refers to all objects / systems moving at constant velocity

Note: graphically all forces forms a closed polygon

ΣF = 0 ; ΣFX=0 ; ΣFY = 0 : R = 0

NEWTON’S LAWS OF MOTIONNEWTON’S SECOND LAW If a net external force acts on a body, the body accelerates. The direction of acceleration is the same as the direction of the net force. The mass of the body times the acceleration of the body equals the net force vector.

In Symbols,

By Components;

NEWTON’S LAWS OF MOTIONNEWTON’S THIRD LAW If body A exerts a force on body B ( an “action”), then body B exerts a force on body A ( a “reaction”). These two forces have the same magnitude but are opposite in direction. These two forces act on different bodies.

What is a Force?

Unit of a Force

*One newton is the amount of net force that gives an acceleration of 1meter per second squared to a body with a mass of 1 kilogram.

Relationship Between Mass & Weight

Kinds of Forces1.Weight, W – force due to earth’s gravitational attraction which is always acting from the center of gravity (c.g.) downward.

2. Tension , T – a pulling force exerted on an object by a rope, cord, cables, etc.

3.Compression, C – a push applied to a body using a rod, bar, mast, etc. (directed towards the body or point being considered)

4. Normal Force, N– when an object rests or pushes on a surface, the surface exerts a push on it that is directed perpendicular to the surface

Kinds of Forces

Cθ

5. Friction Force, f – force acting between the body and its surface of contact which is parallel but opposite to the direction of motion.

Kinds of Forces

Types of Friction:1. Static Friction, fs – exists when the body is at

rest but has the tendency to slide.2. Kinetic Friction, fk – opposing force when

the body is in motion.

where: f- friction force n- normal force μ – coefficient of friction

f α n or f = μ n

Steps in Solving Problems:Make a diagram of the whole structure

being considered.Draw a separate force diagram / Free –

Body Diagram, FBD FBD – is one part of the whole

structure on which known and unknown forces act. (Point of concurrency )

Super impose x and y axis on FBD.

Apply ΣF =0 -[for system / body in equilibrium]

ΣF = ma -[for system / body with acceleration]