Chapter 15 Energy Energy and Work Energy: The ability to do work

Chapter 15

Energy

Energy and Work

Energy: The ability to do work.

Work

The transfer of energy as the result of motion.

(Unit of Work is the Joule)

Work = Force x distanceW = F x d

Joule (J)

Unit of Energy and Work. W = F • d

Joule = Newton • meterJ = (kg • m/s²) • m

Kinetic Energy (KE)

Energy that appears in the form of motion.

Kinetic Energy (KE)

KE = ½ mv2

m

A 70.0-kilogram daemon is walking at a speed of 2.0 m/s. What is his kinetic energy?

Given: m = 70.0kg v = 2 m/s

Find: KE = ?

KE = 140J

Equation: KE = ½ mv2

Solve: KE = ½ (70.0kg)(2 m/s)2

Potential Energy (PE)

Energy that an object has as the result of its position or condition.

Gravitational Potential Energy (GPE)

An object's gravitational potential energy depends on its

mass, its height, and the acceleration due to

gravity.

m

h

PE = mghm = mass

h = height g = acceleration due to gravity(9.8m/s2)

Suppose the diver at the top of a 10.0-meter-high diving platform has a mass of 50.0 kilograms.

Given: m = 50.0 kg h = 10 m

g = 9.8 m/s2

Find: GPE = ?

GPE = 4900J

Equation: GPE = mgh

Solve: GPE = (50.0kg)(9.8 m/s2)(10m)

Elastic Potential Energy

The potential energy of an object that is stretched or compressed.

Forms of Energy

The major forms of energy are mechanical energy, thermal

energy, chemical energy, electrical energy, electromagnetic energy,

and nuclear energy.

Mechanical Energy

Kinetic Energy and

Potential Energy

ME = KE + PE

Thermal Energy

The total potential and kinetic energy of all the microscopic

particles in an object

Chemical Energy

The energy stored in chemical bonds.

Electrical EnergyEnergy associated with

electric charges.

Electromagnetic EnergyForm of energy that travels through

space in the form of waves.

Nuclear Energy

The energy stored in atomic nuclei.

Nuclear Fission

NuclearFusion

NuclearFusion

HomeworkMath Practice

Page 448, Probs:1-3

Section 15.1WorksheetDue: 4/29/10

Law of Conservation of Energy

•Can change from one form to another.• Can never be created or destroyed. •Total energy of the universe remains the same.

Energy:

Mechanical Energy = Potential Energy + Kinetic Energy

E = PE + KE

KE = 0PE = max

KE = 0PE = maxKE = max

PE = 0

Pol

e V

ault

Kinetic Energy

ElasticPotential

Energy

Kinetic Energy

Gravitational Potential Energy

E - Energym - mass c – speed

oflight

Work

PE

KE + PE

KE + PE

Homework 15-2

Section 15-2WorksheetDue: 4/7/09

Nonrenewable EnergyA source of energy that exists in limited quantities and, once used, cannot be replaced except over the

course of millions of years.

Nonrenewable EnergyNonrenewable energy

resources include oil, natural gas, coal, and uranium

Renewable Energy

A source of energy that can be replaced in a relatively

short period of time.

Renewable Energy

Renewable energy resources include hydroelectric, solar, geothermal, wind, biomass, and, possibly in the future,

nuclear fusion.

Hydroelectric

Solar

Geo

ther

mal

Win

d

Biomass

Homework 15-3

Section 15-3Worksheet

D: Due: 4/8/09

Homework 15-3Section 15-3Worksheet

D: Due: 4/8/09F: Due: 4/7/07D Test: 4/9/08

F Test: 4/11/08

Homework 15 -3Section 15-3

Word-wise/MathWorksheetsDue: 5/5/10

D Test: 5/6/10E Test: 5/7/10

Temperature and Heat

Temperature: The measure of the average kinetic energy of the particles

in a sample of matter.

Thermal Energy

The total energy of the particles in a material.

25ºC

25ºC

Heat

The flow of Thermal Energy.

Heat is the flow of Thermal Energy from an area of

High Temperature to one of

Low Temperature.

Thermal Pollution

Waste you can’t see!!!

Thermal Pollution: Occurs when waste heat significantly changes the

temperature of the environment. 

Adding warm water to lakes, rivers and oceans can change the environment.

How?

Homework 5-2

Section Wrap-upPage: 137

Section Wrap-upPage: 140

Due: 11/7/05

Projects Due

Tomorrow11/04/05

Measuring Thermal Energy

      Temperature

Type of Material

Mass of Material

MaterialWater Metal

Specific Heat

Specific Heat [C, J / (kg • K)]The amount of energy it takes to it

takes to raise the temperature of 1 kg of material 1 Kelvin. ( K = C )

It takes 4184 joules of energy to raise the temperature of 1 kg of water, 1C.

Material Specific Heat

Water 4184 J / (kg • K)Alcohol 2450 J / (kg • K)

Aluminum 920 J / (kg • K)Graphite(Carbon) 710 J / (kg • K)

Sand 664 J / (kg • K)Iron 450 J / (kg • K)

Copper 380 J / (kg • K)Silver 235 J / (kg • K)

Calculating Thermal Changes

Specific Heat - C

Change in Thermal Energy - QMass - m

Change in Temperature - T

Q = m • T • C

T = Tfinal - Tinitial

Example: Mr. Clune wants to bring 1 kg of water to boiling for his

afternoon tea. The temperature of the water out of the tap is 10C. How much Thermal Energy does he have

to add to the water?

Given: m = 1 kg Find: Q = ?Tinitial = 10C Tfinal = 100CC = 4184 (J / (kg • C ) )

Equation: Q = m • T • C Q = m • (Tfinal - Tinitial) • C

Solve: Q = (1 kg) • (100C -10C) • 4184(J/(kg • C)Q = (1 kg) • (90C) • 4184 (J/(kg • C)

Q = 377,000 J or 377 kJ

Example: Do the same problem as the one above but use sand instead.Given: m = 1 kg Find: Q = ?

Tinitial = 10C Tfinal = 100CC = 664 (J / (kg • C ) )

Equation: Q = m • T • C Q = m • (Tfinal - Tinitial) • C

Solve: Q = (1 kg) · (100C -10C) · 664(J/(kg.C)

Q = 60,000 J or 60 kJ

Homework 5-4Practice Problem: 1-2

Page:143Section Wrap-up

Page: 144Due: 11/09/05

Test on 11/15/05

Homework 5-5

Vocabulary: 1-10Page:147

Review Questions:1-25Page: 148-149Due: 11/22/04Test: 11/23/04