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Chapter 4 Laws of Motion and Forces

Chapter 4 Laws of Motion and Forces. Goals: Newtons Laws, Inertia and mass, Mass vs Weight, Free Body diagrams, Fg , Fn , Fy , Fx , Ff , coefficients of friction. What causes a change in velocity?. Unbalanced force Vector Acceleration Sum of forces and the direction

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Chapter 4 Laws of Motion and Forces

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  1. Chapter 4 Laws of Motion and Forces Goals: Newtons Laws, Inertia and mass, Mass vs Weight, Free Body diagrams, Fg, Fn, Fy, Fx, Ff, coefficients of friction

  2. What causes a change in velocity? • Unbalanced force • Vector • Acceleration • Sum of forces and the direction • Types of forces include contact forces and field forces • Force diagram uses arrows to represent the vector where length represent the magmitude • Free Body diagram arrows represent force directions and magnitudes x and y coordinates • SR-1 pg 124

  3. Newton’s First Law of Motion • An object will remain at rest or in constant straight motion until an unbalanced force acts on the object • Unbalanced force – net force ƩF • Unbalanced forces cause an acceleration- change in direction or speed • Change in Velocity • Inertia – resistance to an acceleration • Mass – measure of inertia and of matter • PP – A pg 124

  4. Newton’s Second Law • A Force is directly related to mass and directly related to an acceleration • F = m × a • the unit for force F = m x a • = kg m/s2 • = N • PP – B pg 128 • PP – C pg 132

  5. Newton’s Third Law • Newton’s third law – for every action there is an equal and opposite reaction • Forces occur in pairs • Why? • Inertia • even field forces occur in pairs ex: accelerate towards Earth and Earth accelerates Tides

  6. Weight • Weight- force of attraction toward Earth • depend upon mass and distance from Earth • weight = mass x acc due to gravity • = kg x 9.81 m/s2 • = N

  7. Normal Force • Normal force = force on a surface perpendicular to the surface Fn • 3 situations • object laying flat Fn = FgFg = m g • object on a sloping surface Fn = FyFy =FgcosƟFx = FgsinƟ • object laying flat being pulled at an angle Fn = Fg – Fy because Fn and Fy have to equal FgFy = FappliedsinƟFx = FappcosƟ

  8. Friction • Friction – force that opposes motion when surfaces are in contact • Reduce friction by separating surfaces • Coefficient depends on the surfaces and is a ratio of Ff and the Fn • µ = Ff/FnFsf > Fkf • µs = Fsf/Fn µ = Fkf/Fn • PP – D pg 139 • PP - E #1 pg 141

  9. Think about Forces…………………… • Contact and field forces • Normal force • Component forces Fx and Fy • Forces of friction Fs and Fk • There are forces everywhere! • all over the Universe/Multiverse • Forces are FUN • and a lot of work

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