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SC PHYS 201 - Review

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Phys 201 1nd Edition Lecture13 Outline of Last Lecture I. Potential energy and conservation of energy with potential and kinetic energy. Outline of Current Lecture II. ReviewA. FrictionB. Circular motioni. Arc lengthii. Centripetal accelerationiii. Angular velocityiv. Period and FrequencyC. GravitationD. Worki. Kinetic Energyii. Potential Energyiii. Conservation of energyCurrent LectureFriction:Friction is a resisting force, which means that it works in the opposite direction of the movement of an object. This means that when the net force is calculated, the force of friction is subtracted from the force moving the object. The force of friction is equal to the friction coefficient (μ) times the normal force of the object.Ff=μN  Ff=μmgCircular motion:Circular motion can be measured a number of different ways;Arc length (s): the distance between two points on the outside of a circle. This is measured by multiplying the radius of the circle by the angle of the distance between the two points (θ).These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.S=rθ ΔS=rΔθCentripetal acceleration (ac): the acceleration at which an object moves around the center point of a circle. ac=V2/rAngular velocity (ω): the speed at which an object changes position in reference to the center ofa circle.ω=Δθ/ΔtPeriod (T) and frequency (f): period is the amount of time that it takes for circular motion to complete one revolution or one full circle. The frequency in the number of revolutions or part ofa revolution completed in one second, and is therefore the inverse of the period (1/T)All of these measurements can be converted to solve for a number of different properties of circular motion. Knowing how to convert certain attributes of a circle can help in solving force ofcircular motion problems. Ω= Δθ/Δt = V/r = 2πf = 2π/T = (ΔS/Δt)ac = V2/r = (rΩ)2/r = rΩ2Fnet= mac = m(V2/r) = m(4π2r/T2)Gravitation:Gravity works as an attractive force between two bodies and it is universal. The coefficient of gravitation is constant for any given mass (6.67x10-11), and the attractive force between two objects is proportional to the masses involved and the distance between the centers of the two objects.F=(GM1M2)/r2Because we know that the force of gravity on earth is 9.81m/s2, most gravitational problems deal with a ratio of a mass compared to earth. Conveniently, this means that to calculate the force of gravity of another object, just multiply the value of the difference in mass over the difference in radius squared by 9.81. For example, if a planet has a mass that is 2x earths mass and a radius that is 3x Earth’s radius, then to solve for the force of gravity on this planet, you would multiply (2/32)(9.81).Work:When a force moves an object, that force is said to have done work. Work itself is not a vector. It is, however, the product of two vectors (dot product), specifically force and displacement. This means that work is the product of force, displacement, and the cosine of the angle between the two.W=fxCos(θ)Kinetic Energy:Kinetic energy (Ke) is energy of work in terms of motion. The work of an object with kinetic energy corresponds to the change in kinetic energy.Ke=.5mV2W=Kef - Kei  W=.5mVf2 -.5mVi2Potential Energy:When an object is at rest and no movement is visible, it still has stored energy, which is called potential energy (Pe). Because there is no motion with potential energy, velocity is obsolete. Therefore, potential energy is calculated by multiplying weight of an object by the displacement of an object, typically in terms of height (h).Pe=mghConservation of energy:Energy cannot be created or destroyed, only transformed. This means if an object is at rest, then falls to the ground, the amount of kinetic energy when it hits the ground must be equal to the amount of potential energy the objects had when it was at rest. 0=ΔKe + ΔPe  0=Kef -Kei + Pef -Pei  Kei+Pei = Kef + Pef  (0.5mVi2)+ (mghi) = (0.5mVf2)+


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