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##### Ch. 10 Energy, Work, and Simple Machines

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**Ch. 10Energy, Work, and Simple Machines**Milbank High School**Sec. 10.1**• Objectives • Describe the relationship between work and energy • Display an ability to calculate work done by a force • Identify the force that does work • Differentiate between work and power and correctly calculate power used**Energy**• The ability to produce change in itself or the environment • Mechanical Energy • Ability to do work • Potential Energy • Stored energy • Kinetic Energy • Energy of motion**Kinetic Energy**• Utilizes motion equations and Newton’s second law of motion • Produces**Work**• Transfer of energy by means of forces • 1/2mv1 – 1/2mv0 = Fd so… • K = 1/2mv2 so… • W = Fd or… • K1 – K0 = W or ∆K = W • Measure in Joules (kg·m2/s2)**Problems**• Example Problem Pg. 226 • Calculating Work Practice Problems Pg. 227**Calculating work at an angle**• W = Fd cos Ө • Example Problem Pg. 228 • Force and Displacement at an Angle**Power**• Power is the rate of doing work, or the rate at which energy is transferred • P = W/t • Power is measure in watts (1 joule of energy transferred in one second)**Sec. 10.2**• Obejctives • Demonstrate knowledge of why simple machines are useful • Communicate an understanding of mechanical advantage in ideal and real machines • Analyze compound machines and describe them in terms of simple machines • Calculate efficiencies for simple and compound machines**Machines**• Ease the load by changing either the magnitude or the direction of a force as it trasmits energy to the task • Basically….make tasks easier • Wi • work input, the work you do • Wo • Work output, the work the machine does**Mechanical Advantage**• The ratio of resistance force to effort force • Fr/Fe • Hopefully its greater than 1 • Effort force • The force you exert on a machine • Resistance force • Force exerted by the machine**Ideal Mechanical Advantage**• Ideal Machine: all energy transferred, or in other words W0 = Wi Ideal Mechanical Advantage = de/dr Measure distances….with MA, you measure the forces**Efficiency**• An ideal machine has equal output and input • Dpes it really ever happen? • Efficiency can be defined as W0/Wi x 100 (for a percent) • Or…MA/IMA x 100 • Efficient machines have an MA close to the IMA**Simple Machines**• Lever • Pulley • Wheel and Axle • Inclined Plane • Wedge • Screw**Compound Machines**• Consists of two or more simple machines • The resistance force of one becomes the effort force of the other • Example Problem Pg. 237 • Bicycle Wheel