Phys 201 1nd Edition Lecture 12 Outline of Last Lecture I. Calculating work and kinetic energyOutline of Current Lecture II. Stored energyA. Potential EnergyB. Gravitational Potential EnergyIII. Work and Potential EnergyIV. Conservative ForceV. Conservation of EnergyA. Solving Transformed EnergyCurrent LectureStored Energy:When something is at rest and no movement is visible, there is still energy. This is stored energy, also called potential energy. When you drop an object that was previously at rest, the stored energy of the object becomes kinetic energy. Gravitational Potential Energy:There are several types of potential energy, depending on the position of the object. When the stored energy of an object is a result of the height of an object, the object has gravitational potential energy. Mass and height both have a major effect on gravitational potential energy. The greater the mass of an object, the greater the gravitational potential energy. Similarly, the higher an object is lifted (the greater the value of h), the greater the gravitational potential energy. As an equation, this relationship is expressed as;PE=mghWork:Remember that in terms of energy, work can be described as a transfer from one kind of energy to another. This means that work can be done with potential energy, even though no movement is visible. Because energy is measured in force times displacement, the equation for work in terms of a change in potential energy is;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.W=ΔPe =Pef - Pei= mghf - mghiIn this case, displacement is measured by the height of the object, or h. Because we are working with displacement, potential energy can be negative. Conservative Force:The amount of work done by gravity is independent of the path that an object takes. This is known as a conservative force. If an object moves in a closed path, meaning that its displacement is 0, and the net value of the force moving the object is equal to 0, then the force is a conservative force. Example: B CPath 1Path 2 Path 3A DIf you assume that gravity is moving an object of a constant mass along any one of these paths, then no matter which path the object follows, the net force required to move the object through any of these paths completely will be 0. Therefore, the net force of all three paths will be equal.Conservation of Energy:The law of conservation of energy states that; “Energy can neither be created, nor destroyed. It can only be transformed.” This means that if you drop an object that was previously at rest in your hand, the amount of stored potential energy when the object was at rest, is equal to the amount of kinetic energy the object has when you drop it. In terms of potential energy (Pe) to kinetic energy (Ke), for conservative forces, conservation of energy can be expressed as; 0=ΔKe + ΔPe0=Kef -Kei + Pef -PeiKei+Pei = Kef + Pef(0.5mVi2)+ (mghi) = (0.5mVf2)+
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