 # Chapter 13 WORK & ENERGY.

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Chapter 13 WORK & ENERGY

TN Standards CLE – Demonstrate the relationship among work, power, and machines CLE – Investigate the Law of Conservation of Energy

Bellwork What is Work?

Work, Power, and Machines
Work is conducted only when an applied ( net ) force results in the change in position of an object Work is measured in Joules ( J ) Work is calculated by multiplying force and distance ( over which the force is applied ) W = F x d

Work, Power, and Machines
Power is the amount of work conducted over a certain time interval P = W / Δt Power is measured in Watts

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

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 = hmg h is height ; g is gravity; m is mass 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