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Chapter 13 WORK & ENERGY TN Standards • CLE 3202.4.3 – Demonstrate the relationship among work, power, and machines • CLE 3202.2.6 – Investigate the Law of Conservation of Energy Bellwork • What is Work? Work, Power, and Machines • Work is conducted only when an unbalanced force results in the change in position of an object • Work is measured in Joules ( J ) = N x m • Work is calculated by multiplying force and distance ( over which the force is applied ) –W=Fxd Work, Power, and Machines • Power is the amount of work conducted over a certain time interval • P = W / Δt • Power is measured in Watts ( W ) = Joule/sec Work, Power, and Machines • Machines help to do work by changing the size of an input force, the direction of a force, or both • Different forces can do the same amount of work – Figure 3 ( a box lifted vs a box pushed up a ramp ) Simple Machines • The six types of simple machines are: – Simple lever – Wheel and axle – Pulley – Simple inclined plane – Wedge – Screw Compound Machines • A combination of any of those six simple machines • Example – SCISSORS • Combination of lever and wedge Mechanical Advantage Mechanical Advantage • Example Bellwork • What is Energy? What is Energy? • Energy is a property of an object due to its motion or its position • When work is done, energy is transferred or transformed from one system to another – Carry a tennis ball up in the stadium – You add potential energy to it by carrying it up What is Energy? • Energy is measured also in Joules ( J ) • Potential energy – energy of position – PE = hg – h is height ; g is gravity – Height is relative • Kinetic Energy – energy of motion – KE = ( ½ ) mv2 – m is mass ; v is velocity Other Forms of Energy • Mechanical energy • Non-mechanical energy – ( atomic level ) • Chemical reactions involves chemical energy ( a form of potential energy ) – Sun gets energy from nuclear reactions • Electrical energy ( stored in electric fields ) Conservation of Energy • Energy easily changes from one form to another ( battery ) • PE can become KE ( tennis ball dropped from the top of stadium ) – Vice-versa ( projectile shot / reaches max height ) • Law of Conservation of Energy? – ( neither created nor destroyed ) Roller Coaster Example Thermodynamics • For any system, the net change in energy equals the energy transferred as work and heat • Efficiency ( how much energy/work you get out of a machine or process compared to how much is put in ) – Internal Combustion Engine