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How is Work and Power Related? Chapter 5 Work and Power Goals: define and calculate work, energy, kinetic energy, potential energy, power and use the concept of conservation of energy

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What is Work? Section 5.1 Work is a transfer or conversion of energy transfer occurs when a force is applied in the direction of the force force = mass x acceleration (g) transfer occurs when a force is applied in the direction of the force force = mass x acceleration (g) conversion occurs from one form of energy to another conversion occurs from one form of energy to another mechanical, thermal, electrical, radiant, nuclear and chemical mechanical, thermal, electrical, radiant, nuclear and chemical W = F x d W = F x d cos θ W = F x d W = F x d cos θ

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Simple Machines demonstrate the concept and calculations of Work Simple Machine- device that makes work easier multiply force OR distance multiply force OR distance Increasing force or distance are at the expense of the other variable Energy is conserved in an ideal situation no friction Work in would equal Work out in another words F x d (in) = F x d (out) Work in is done on the machine and Work out is done by the machine

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R ---2m-----f m E R ---2m-----f m E MA = 2 MA = 2 R= 40N f E = 20N R= 40N f E = 20N MA = 2 MA = 2 MA = Fr / Fe or MA = Fr / Fe or MA = Xe / Xr MA = Xe / Xr Levers include 1 st, 2 nd, 3 rd, classes, wheels and axels and pulleys Pulley- grooved wheel and a rope MA= the number of strands supporting resistance

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Inclined Planes include ramps, wedges and screws Gears- toothed wheels MA = ratio of teeth of each gear increase force or speed of rotation Efficiency- ratio of work out to work in eff = W out / W in eff = W out / W in

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What is Energy? 5.2 Energy – ability to cause a change to do work work = transfer of energy to do work work = transfer of energy 6 forms of energy and two states of energy Kinetic – motion W = F x d W = F x d = m x a x ΔX a ΔX = vf² - vi² / 2 = m x a x ΔX a ΔX = vf² - vi² / 2 = m x vf² - vi² / 2 = m x vf² - vi² / 2 = ½ m v² = ½ m v² increase mass vs increase velocity v² increase mass vs increase velocity v²

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Work – Energy Theorem transfer of energy by a force through a distance transfer of energy by a force through a distance transfers Kinetic Energy transfers Kinetic Energy Work = ΔKE Work = ΔKE = KE f – KE i = KE f – KE i Units KE = ½ mv² = kg m²/s² = kg m²/s² = N m = N m = J = J

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What is Potential Energy? Potential Energy – state of energy where a change is stored position relative to a measured height position relative to a measured height gravitational potential energy gravitational potential energy PE = m g h weight = m g PE = m g h weight = m g = kg m/s² m = N = kg m/s² m = N = N m = N m = J = J

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Elastic potential energy – energy stored in an object stretched or compressed Spring ex. spring scale PE elastic = ½ k x² PE elastic = ½ k x² k = spring constant k = spring constant x = distance stretched x = distance stretched

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How is Energy Conserved ? Conserved – energy is not gained or lost within a system only converted or transferred Mechanical Energy is the sum of the KE and the PE in a system the exception is friction that converts some ME into heat that is nonmechanical the exception is friction that converts some ME into heat that is nonmechanical ME i = ME f KE + PE = KEtotal ME i = ME f KE + PE = KEtotal ½ mv² + mgh = ½ mv² + mgh ½ mv² + mgh = ½ mv² + mgh ex. Falling rock PE to PE+KE to KE ex. Falling rock PE to PE+KE to KE

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What is the Rate at which work is done? Power – the rate at which work is done or energy converted or transferred P = ΔW / t P = ΔW / t = F x d / t = F x d / t = F x v = F x v mgh / t or ½ mv² / t mgh / t or ½ mv² / t units P = W / t units P = W / t = J / s = J / s = watts 1000 w = kw = watts 1000 w = kw 1 hp = 746 w 1 hp = 746 w

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YOU have the POWER To get the WORK done And Accelerate on this next Exam

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