forces

Chapter 2
Forces
To study the effect of forces acting on particles.
2.1 Equilibrium of a Particle
2.2 Free Body Diagram
2.3 Force Vectors
2.4 Forces in a Plane
2.5 Forces in Space

Expected Outcomes
• Understand the condition for a particle to be in static equilibrium • Able to construct free body diagrams
• Able to solve for the forces acting on a static particle

2.1
Equilibrium
of a Particle

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2.1.1 Condition for the
Equilibrium of a Particle
• Particle is at equilibrium if it is
a) At rest
b) Moving at constant a constant velocity

2.1.1 Condition for the Equilibrium of a Particle
(a) Equilibrium at rest
• Newton’s first law of motion
∑F = 0 where ∑F is the vector sum of all the forces acting on the particle Even Univ.
Graduates

(a) Equilibrium at rest

• Newton’s Law of
Motion
• 1st law – a particle originally at rest, or moving in a straight line with constant velocity, tends to remain in its state provided the particle is not subjected to an unbalanced force.

http://www.jameslogancourier.org/index.php?blogid=1&archive=2006-3-21

2.1.1 Condition for the
Equilibrium of a Particle
(b) Equilibrium at motion
• Newton’s second law of motion
∑F = ma
• When the force fulfill Newton's first law of motion, ma = 0 a=0 therefore, the particle is moving in constant velocity or at rest

2.1.1 Condition for the Equilibrium of a Particle
Forces in equilibrium

2.1.1 Condition for the
Equilibrium of a Particle
• Methods to solve for force equilibrium:
• graphical solution yields a closed polygon


• algebraic solution R   F  0

2.2 Free Body Diagram

2.2 The Free-Body Diagram (FBD)
• ~ the best representation of all the unknown forces (∑F) which acts on a body
• ~ a sketch showing the particle “free” from the surroundings with all the forces acting on it
• Two common connections which are usually replaced as forces in FBD
• Spring
• Cables and