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.

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 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

• Power is the amount of work conducted over a certain time interval

• P = W / Δt

• Power is measured in Watts

Work, Power, and Machines

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