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Work, Kinetic Energy, and Potential Energy The Nature of Work – In the everyday sense, work involves pushing, pulling, lifting, etc. • Work – is the measure of the amount of energy that is transferred when a certain force acts through as certain distance to do some job. Work & Transfer of Energy Idea • 1. Horizontal Force is applied to a dynamics cart for a certain distance – work is done, i.e. energy is transferred to the cart. The cart now has kinetic energy. • Note: When a force is applied at an angle, cart moves horizontally. The only force which does useful work on the cart is Fh=Fcosq 2. Work, Energy Transfer, and Potential Energy e.g. lifting an object (bricks) • When objects are lifted, work is done i.e. a certain force is exerted through a certain distance. Energy is used up (transferred) to get the job done. • But the kinetic energy of the bricks is zero, they are at rest. Where did the energy go? We say that it has been transformed into “potential energy” which is stored inside the bricks. • Potential Energy – energy that is stored in an object because of its condition or position. • E.g. When we stretch out or push in a spring, we do work on it (i.e. transfer energy to it) We say this work goes toward increasing the potential energy of the spring. • In general, any time work is done, energy is transferred to an object, and increases its kinetic or potential energy. Formula for Calculating Work Done 1. Work is to applied force. 2. Work is to distance moved. • 3. Work is not related to time; whether you do a job fast or slow makes no difference, it is still takes the same amount of energy because it’s the same job. So WFd W = kFd (F = Newtons, d = metres) • Units for Work – basic unit is the Nm (Newton metre), called a joule (J) • 1 J = amount of work done when a force of 1 N acts through a distance of 1 m. This conveniently eliminates the “k” in the equation so