Introduction to Statics Discussion topics: Newton’s 3 laws of motion Translational equilibrium Rotational equilibrium Scalars/vectors

Free Body Diagrams Statics Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics The analysis of loads (force, torque, moments) on systems in a state of rest or uniform motion (i.e. constant velocity)

Initially, at least, this is a statics problem

Newton’s 3 Laws of Motion

Free Body Diagrams Statics Principles Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Newton’s First Law of Motion (law of inertia): An object in a state of rest or uniform motion (constant velocity) will continue to be so unless acted upon by an unbalanced external force.

Free Body Diagrams Statics Principles Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Newton’s Second Law of Motion: The acceleration of an object is proportional to the net force acting on the object and inversely proportional to the object’s mass Force = Mass x Acceleration

Free Body Diagrams Statics Principles Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Newton’s Third Law of Motion: (law of interaction) For every action force, there is an equal and opposite reaction force

Equilibrium Static Equilibrium: Free Body Diagrams Equilibrium Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Static Equilibrium: A condition where the external forces acting on a body are balanced. The body remains at rest or continues at a constant velocity

Free Body Diagrams Equilibrium Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Translational Equilibrium: The state in which the vector sum of all forces = 0. The body remains at rest, or continues moving at constant velocity.

Equilibrium Rotational Equilibrium: Free Body Diagrams Equilibrium Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Rotational Equilibrium: The state in which the sum of all the torques = 0. The system does not rotate. Clockwise moments = counterclockwise moments about a pivot point. Remember M = d x F

Statics Principles Free Body Diagrams Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Scalar Quantities: A physical quantity that has magnitude only ©iStockphoto.com ©iStockphoto.com

Free Body Diagrams Statics Principles Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Vector Quantities: A physical quantity that has both a magnitude and direction

Forces illustrated, or “Why we follow safety rules and wear protective gear”

What Is a Force? The pushing or pulling interaction of objects Free Body Diagrams What Is a Force? Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics The pushing or pulling interaction of objects A vector quantity defined by its known magnitude, direction A 45 lbf 21.8°NE

Force Units U.S. System (U.S. Customary Units) Free Body Diagrams Force Units Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics U.S. System (U.S. Customary Units) pound (lb), sometimes called pounds-force (lbf) Metric System (S.I. Units) newton (N) Conversions between Unit Systems 1lb = 4.448 N 1N = 0.2248 lb

Static Equilibrium Force Principles Free Body Diagrams Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics Static Equilibrium Force Principles Forces always occur in pairs acting on two different objects. (Newton’s 3rd law). Force pairs act in opposite directions and have the same magnitude.

Force Components Free Body Diagrams Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics A single force can be replaced by component forces if their combination produces the same effect as the original force. a Fa Fay Fax a

Free Body Diagrams Resultant Force Principles of EngineeringTM Unit 4 – Lesson 4.1 - Statics A single force that has the same effect as two or more concurrent forces 7lbf Resultant force = 2lbf 5lbf 3lbf Resultant force 5lbf 2lbf =