Chapter3-Equilibrium of a Particle

# Chapter3-Equilibrium of a Particle - Equilibrium of a...

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PCS211 – Physics II: Mechanics Equilibrium of a Particle in 2D Newton’s Laws Lecture 6-7 (Chapter 3) Dr. Marina Milner-Bolotin Check Blackboard for course web site!

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PCS211 – Physics II: Mechanics Part I: Lecture 6 Goals for Lecture 6: Short tour into Newton’s three laws of motion. Learn how to draw Free Body Diagrams (FBD) and identify and label forces Review Newton’s Laws of Motion (especially the 1 st and the 3 rd ) Learn how to apply equations of equilibrium to solve 2-D problems. 2
PCS211 – Physics II: Mechanics 24/05/10 3 Force: The measure of interaction between two objects (pull/push). Vector Vector – has magnitude & direction, [F] is Newton Newton , N N Mass: The measure of how difficult it is to change object’s velocity (sluggishness or inertia). Scalar Scalar , [m] is a kilogram, kg Weight: The force the Earth is pulling the object with. Vector Vector has magnitude & direction, [ w ] is Newton, N (or pound Lb )

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PCS211 – Physics II: Mechanics 24/05/10 4 Force as a Measure of Interaction Between Objects F box on spring F spring on box Since the force is a measure of interaction between TWO objects, to describe any force properly, you must identify these objects . I do not want to hear the “G” word anymore. Instead of Gravity say the Force of the Earth on an object.
PCS211 – Physics II: Mechanics 24/05/10 5 Net Force: F net One object can interact with many. So multiple forces can be exerted on it. A NET FORCE NET FORCE (F (F net net ) ) is a resultant force acting on an object. To find the To find the F F net net you you have to add up all the have to add up all the

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PCS211 – Physics II: Mechanics 24/05/10 6 Newton’s 1 st Law: The Law of Inertia 1. An object at rest remains at rest as long as no F net acts on it. 2. An object moving with const velocity continues to move with the same speed and in the same direction ( same same v v ) as long as no net force acts on it. 3. Every object continues in its state of rest, or uniform motion in a straight line, unless it is compelled to change compelled to change that state by unbalanced forces that state by unbalanced forces impressed upon it Inertia is a property of objects to resist changes is motion! An additional force is NOT required to keep a cart moving with a constant speed on a frictionless air track!
PCS211 – Physics II: Mechanics Forced in 1D: PhET Sims 7

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PCS211 – Physics II: Mechanics 24/05/10 8 Why Is the 1 st Law So Important? 1. The 1 st law holds true only in the non-accelerating reference frames which will be called INERTIAL REFERENCE FRAMES (IRF) 2. Newton’s laws work only in IRF, for other frames of reference modifications must be made! 3.
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Chapter3-Equilibrium of a Particle - Equilibrium of a...

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