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Chap.#3: Statics of Particles

Chap.#3: Statics of Particles. Particle Assumption Modeling of Problem Free Body Diagram: FBD Newton’s Law of Motion 1 st Law 2 nd Law 3 rd Law. Particle Assumption:. The size and shape of object are negligible . Thus, mass of particle concentrate at a point .

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Chap.#3: Statics of Particles

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  1. Chap.#3: Statics of Particles • Particle Assumption • Modeling of Problem • Free Body Diagram: FBD • Newton’s Law of Motion • 1st Law • 2nd Law • 3rd Law

  2. Particle Assumption: • The size and shape of object are negligible. • Thus, mass of particle concentrate at a point. • Note All forces acting on object are concurrent forces. That is, All forces act at a point. N T W

  3. Problem Solving Strategy: • Physical Model: • Transformation of actual problem into simpler one • Assumptions • Using Free Body Diagram: FBD • Mathematical Model: • Newton’s Law: • F=0 and Mo=0 (Select coordinate System) • Set of equations to be solved • Solution of Equations: • Computational Tools: Maple, Matlab, Prog. • Conclusions: Does answer make sense?

  4. Newton’s Laws of Motion Law #1: Body is in Equilibrium • Body will remain at rest or continue to move with same speed (accel.=0) and direction unless an unbalanced force is acted on body or particle.

  5. Newton’s Law of Motion Law #2: Non-equilibrium • Change of motion of a body is proportional to the next force imposed on the body and is in direction of net force. • For Equilibrium it is required that,

  6. Newton’s Law of Motion • Law #3: Action & Reaction • If one body exerts a force on a second body, then second body exerts a force on the first body that is equal in magnitude, opposite in direction and collinear (same line of action).

  7. Definition of Free-Body Diagram • A free-body diagram is a sketch of an object or connected group of objects, modeled as a single particle, that isolates the body from its environment or surrounding bodies and represents the interaction of its environment by external forces.

  8. Drawing a Free-Body Diagram • Step 1: Imagine particle “FREE” from surroundings. • Draw sketch of external boundary of body. • Step 2:Indicate all forces, known & unknown • If direction of force is unknown then assumed a direction. • Magnitude of a force is always positive, if answer is negative, the minus sign indicates that sense is opposite to the assumed earlier. • Step 3: For each FBD Newton’s Laws of equilibrium must be used.

  9. Example 1: Tension Cables • Determine the tension in cords AB & AD for equilibrium of the 10Kg block. B D A C

  10. Example 2: • Determine the tension in cables A & B for equilibrium if traffic light weights 200lb B A

  11. Example 3: Normal Force • Prob. (3.3) find the normal forces at points NA and NB. The weight of cylinder is W=500lb. Show the FBD and steps. y A B x

  12. Example 4: • Problem 3.2: Block A rest on a smooth (frictionless) surface. If the mass of the block is 100Kg, determine the force exerted on the block by the surface and the force P required to prevent the motion of the block. P 3 y x 8

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