Energy Basics

Mr. ClarkBethpage HS

AP Environmental Science

Energy Basics

Energy Work Power First Law of Thermodynamics Second Law of Thermodynamics Kinetic energy Potential energy

Energy Basics

First Law Efficiencies Second Law Efficiencies Thermal efficiency Electrical resistivity Conservation The hard path versus the soft path

Energy

Energy is the ability to do work. Energy is measured in units called Joules.

Energy is also measured in calories, BTUs, and ergs.

Electromagnetic Spectrum

Transfer of Energy

Convection Conduction Radiation

Heat from a stove burner causes atoms or molecules in the pan’sbottom to vibrate faster. The vibrating atoms or molecules then collide withnearby atoms or molecules, causingthem to vibrate faster. Eventually, molecules or atoms in the pan’shandle are vibrating so fast itbecomes too hot to touch.

As the water boils, heat from the hot stove burner and pan radiate into thesurrounding air, even though airconducts very little heat.

Heating water in the bottom of a pancauses some of the water to vaporizeinto bubbles. Because they are lighter than the surrounding water, they rise. Water then sinks from the top to replace the rising bubbles.This up and down movement (convection) eventually heats all of the water.

Energy Quality

Work

Work is force times distance. W = F x d The unit of work is a Newton-meter.

A Newton-meter is called a Joule (J).

Power Power is the rate that energy is used. Power is equal to work / time. P = W/t One joule / second is a watt. Electrical Power can also be calculated

by another formula. Electrical Power = voltage x current. P = V x I watts = volts x amps

First Law of Thermodynamics

Energy is neither created nor destroyed but is always conserved and transformed from one kind to another.

Energy only changes form. You cannot get something from

nothing. Energy in = energy out

Second Law of Thermodynamics

Energy always goes from a more usable form (high quality) to a less usable form. (low quality)

All systems move to maximum entropy.

Kinetic Energy

Kinetic energy is the energy of motion.

KE = ½ mv2 where m is mass and v is velocity.

Potential Energy

Potential energy is stored energy. PE = m x g x h where m is mass, g

is the acceleration due to gravity, and h is height.

First Law Efficiencies

First Law Efficiencies are the amount of energy available without consideration of energy quality.

Second Law Efficiencies

Second Law Efficiencies are the amount of energy available with consideration of energy quality.

Thermal efficiency

Thermal efficiency is the maximum possible efficiency of a heat engine. (Carnot 1824)

Electrical resistivity

Electrical resistivity is what causes electrical energy to be converted to heat energy.

It is like electrical friction.

Conservation

Conservation is saving energy whenever possible.

The hard path vs. the soft path

Hard Path Let energy companies

develop resources. Do away with

regulations so that the market can determine the most efficient use of energy with the least environmental consequences.

Soft Path Develop alternate

energy technologies such as solar, wind, and biomass.

Use diverse technologies.

Be flexible with the use of technologies.

Match the needs of the area.