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Forces and Motion

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What You Will Learn -Newton’s Laws of Motion -Motion Terminology -Sample Problems

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Newton’s Three Laws of Motion Newton’s First Law of Motion – An object at rest will remain at rest and an object in motion will continue in motion at a constant velocity in a straight line unless it is acted upon by a net force. This is often called the Law of Inertia because it implies that any mass offers resistance to a change in its velocity. What are other implications? -No applied force to an object means no change in its velocity. Or, if velocity changes, then there has to be a net force that is making that change. -If there is an acceleration, then there has to be a velocity change and a net force present.

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Newton’s Three Laws of Motion Newton’s Second Law of Motion – An acceleration is directly proportional to the applied force and inversely proportional to the mass of the object. For us; F = ma.ma. What are the implications? -You can not have a force with out an acceleration, since mass of an object does not change. -Force is a vector (has magnitude and direction).

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Newton’s Three Laws of Motion Newton’s Third Law of Motion – States that all forces come in pairs that are equal in magnitude but opposite in direction. To paraphrase; For every action there is an equal but opposite reaction. What are the implications? -You can not have a force with out an acceleration, since mass of an object does not change.

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Types of Forces -System – An object of interest. -Force – A push or a pull. -Contact Force – Physically touching. -Field Force – Exert without contact. -Agent – It is a contact or field force and is specifically affects a given system. -Free Body Diagram – Physical representation that shows the forces acting on a system. -Net Force – Is the vector sum of the forces acting on a system. Symbolized by F net. -Equilibrium – A system in which the velocity remains constant. Note: an object at rest is just a special case of velocity, namely v = 0. -Weight – The gravitational force experience by an object. F g = mg. -Apparent Weight – A weight that is not true weight, but it is one you experience due to your current conditions.

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-Weightlessness – The absents of apparent weight. -Drag Force – The force exerted by a fluid on an object opposing motion through the fluid. Note: air is a fluid. -Interaction Pair – Newton’s Third Law. All forces come in pairs. -Tension – Force exerted by a rope, string, or cable. The rope, string, or cable is generally considered massless. Types of Forces

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Tension T FgFg FaFa T y = T sin T x = T cos y x Wall or attachment point

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Tension T FgFg FaFa T y = T sin T x = T cos y x Wall or attachment point What happens to tension as gets bigger?

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Tension F g = –100 N F ax is the applied force What is the tension in T 1, T 2, T 3, and T 4 ? 90 o T1T1 F g 60 o T2T2 FgFg Fa2Fa2 45 o T3T3 F g Fa3Fa3 30 o T4T4 F g Fa4Fa4 Team Work

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Tension F g = –100 N F ax is the applied force 90 o T1T1 F g 60 o T2T2 FgFg Fa2Fa2 45 o T3T3 F g Fa3Fa3 30 o T4T4 F g Fa4Fa4 F = 0 = T 1 + F g –T 1 = F g T 1 = – F g T 1 = – (100 N) T 1 = 100 N y x y x y x y x Mouse or Enter to Continue

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Tension F g = –100 N F ax is the applied force 90 o T1T1 F g 60 o T2T2 FgFg Fa2Fa2 45 o T3T3 F g Fa3Fa3 30 o T4T4 F g Fa4Fa4 T 1 = 100 N T 2 = 115 N T 3 = 141 N T 4 = 200 N

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Tension m = 1.00 10 3 kg. Find T, no acceleration T F g pulley

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Tension T Fg Fg pulley

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What You Have Hopefully Learned -Newton’s Three Laws of Motion -Motion Terminology -Sample Tension Problems

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END OF LINE And Now, The Crane Problem.

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30 o 100 o mass = 2000 kg Two cranes are holding a load that has a mass that will be given to you by the teacher. Find the value of T 1 and T 2. Show the force diagram and the vector equation needed to solve this problem. T1T1 T2T2

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T 1x = T 1 cos 130 o oo 100 o T1T1 T2T2 Simplified Force Diagram T 1y = T 1 sin 130 o T 2y = T 2 sin 30 o T 2x = T 2 cos 30 o y x

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