Nature of Energy

• Energy is all around you!o You can hear energy as

sound.o You can see energy as

light.o You can feel it as wind and

heat.

• You use energy when you:o hit a softball.o lift your book bag.o compress a spring.o Burn fuel

Nature of Energy• Energy is

involved when:o a bird flies.o a bomb

explodes.o rain falls from

the sky.oelectricity

flows in a wire.

States of Energy: Kinetic and Potential Energy

• Kinetic Energy is the energy of motion.

• Potential Energy is stored energy of position or chemical bonds.

Kinetic Energy• The energy of motion is called

kinetic energy.• The faster an object moves, the

more kinetic energy it has.• The greater the mass of a moving

object, the more kinetic energy it has.

• Kinetic energy depends on both mass and velocity.

Kinetic Energy

K.E. = ½ mass x velocity2

What has a greater affect of kinetic energy, mass or velocity? Why?

Potential Energy• Potential Energy is stored

energy.oStored chemically in bonds of fuel

or food oStored as nuclear energy holding

subatomic particles together oOr stored because of the work done

on it:• Stretching a rubber band.• Winding a watch.• Pulling an arrow back on a bow’s string.

• Lifting a brick high in the air.

Gravitational Potential Energy

• Potential energy dependent on height is called Gravitational Potential Energy (a form of mechanical energy)

Gravitational Potential Energy

• If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board.

• GPE=Weight x Height

• (pounds) x (feet)• or (Newtons) x (meters)

• GPE = (M)(Ag) (H)• M=Kg, Ag =9.8m/sec2,H=m

Kinetic – Potential Energy Conversion

Cars are mechanically pulled to the peak which is the point of maximum potential energy, the car has minimum kinetic energy. As position is exchanged for speed, potential is converted to kinetic energy.

Ball slows down

Ball speeds up

Forms of Energy• The five main forms of energy are:oHeatoChemicaloElectromagneticoNuclearoMechanical

Heat Energy• The internal motion of the

atoms is called heat energy, because moving particles produce heat.

• Heat energy can be produced by friction.

• Heat energy causes changes in temperature and phase of any form of matter.

Chemical Energy• Chemical Energy is required to bond atoms together.

• And when bonds are broken, energy can be released or absorbed

• Exothermic = energy released.

• Endothermic=energy absorbed.

Chemical Energy

• Fossil Fuels and our Food are forms of energy stored in chemical bonds• The Energy came from nuclear

fusion on our Sun and was photosynthesized by plants and stored in plant and animal life

Formation of Fossil Fuels

• Petroleum and Natural gas are both products of millions of years of decomposing Marine life, both animal and plant

• Coal is similar but mostly from terrestrial plant life

Where does Coal come from?

Electromagnetic Energy• Electricity -- carried in

wires• Light -- Each of the colors

of light (ROY G BIV) represents a different amount of electromagnetic energy

• X-rays & Cosmic Rays• TV & Radio waves• Laser light.

Nuclear Energy• When the nucleus

splits (Fission), nuclear energy is released in the form of heat energy and light energy.

• Nuclear energy is also released when nuclei collide at high speeds and join (Fusion).

• MOST CONCENTRATED

Mechanical Energy• When work is done to an object, it acquires energy. The energy it acquires is known as mechanical energy.

Mechanical Energy• When you kick a football, you give mechanical energy to the football to make it move.

Energy Conversion• Energy can be changed from one form to another. Changes in the form of energy are called energy conversions.

• Good Examples on Pages 418-419

Energy conversions• All forms of energy can be

converted into other forms.oThe sun’s energy through solar

cells can be converted directly into electricity(Photovoltaic energy).

oGreen plants convert the sun’s energy (electromagnetic) into the bonds in starches and sugars (chemical energy) using Photosynthesis.

Other energy conversions

oIn an electric motor, electromagnetic energy is converted to mechanical energy.

oIn a battery, chemical energy is converted into electromagnetic energy.

oMechanical energy of water falling can be converted to electrical energy in a generator.

Hydroelectric Power

Forms of Alternative Energy

Energy Conversions• In an

automobile engine, fuel is burned to convert chemical energy into heat energy. The heat energy is then changed into mechanical energy.

Chemical Heat Mechanical

The Law of Conservation of Energy

• Man can neither create nor destroy Energy by ordinary means.oIt can only be converted from one form to another.

oIf energy seems to disappear, then scientists look for it – leading to many important discoveries.

Law of Conservation of Energy

• In 1905, Albert Einstein said that mass and energy can be converted into each other.

• He showed that if matter is destroyed, energy is created, and if energy is destroyed, mass is created.

• E=MC2 • M=mass C=speed of light

Power = measure of Energy• Work = Force x Distance• Rate of doing Work or• Amount of Work/unit of time• Power= Work/Time

• Power = (Force x Distance)/Time

• Power Units = Watts • 1Watt=1Joule/sec or (1N*m/sec)• 1 Kilowatt = 1000 watts• 1 Horsepower = 746 watts

Thermal Energy (Heat) differs from

Temperature

Heat vs. Temperature• Heat content is the TOTAL

KINETIC ENERGY of the particles in a sample

• Temperature is the AVERAGE KINETIC ENERGY of the particles in a sample

Which has more Heat and which has the highest temperature?

Styrofoam• There are thousands

of air bubbles trapped in the styrofoam which slows down the heat flow through the layer

•Insulator

Insulation: How do the Polar Bears stay warm in

the snow? Their dense, fine fir traps an air layer next to

their skin.

Home Insulation• The pink fiberglass

fibers trap air in the mat of insulation preventing heat from escaping in the winter or heat from entering during the summer. Insulation

                                                                                                                                                   

                                     

Highly Insulating Windows

• Two or three panes between inside and outside air

• Insulation is supplied by the Dead Air Space

Image source: Southwall Technologies

Heat Transfer• Occurs three waysoConductionoConvectionoRadiation

• The transfer of heat by direct contact between objects or particles.

• Motion of solid or liquid atoms or molecules carried from particle to particle

• Heat transferred by the movement of molecules within liquid or gaseous substance.

• Warm rises, cool sinks.

• A circular motion begins from warmer areas rising due to decreased density moving toward cooler areas which fall because of increased density.

• Wind and Major Weather patterns are caused and move largely because of these convection currents.

• Heat transferred through space

• MATTER is not needed for radiation

• EXAMPLE: The sun’s rays carrying visible light and UV light causing sunburn.

Radiation• Transfer of heat through

electromagnetic radiation (light from stars or light bulbs).

• Transferred in all directions.• Matter is not required!• Dark or dull objects absorb

more than light or shiny objects do.

Temperature• Temperature is a measure of the average KE of the particles in a sample of matter

Temperature Conversions

• oC to oF: oF = (9/5)oC + 32

• oF to oC: oC = 5/9(oF – 32)• oC to K: K = oC + 273• K to oC: oC = K – 273

Going from Celsius to Fahrenheit

Convert 37 oC to oF.oF = (9/5)oC + 32oF = (9/5)37oC + 32 = 66.6 + 32 = 98.6oF

Going from Fahrenheit to CelsiusConvert 68oF to oC

oC = 5/9(oF – 32)oC = 5/9(68 – 32) = 5/9(36) = 20 oC

Going from Kelvin to CelsiusConvert 310 K to oC

oC = K – 273oC = 310 – 273 = 37oC

Thermal Energy• Which beaker of water has more thermal

energy?o B - same temperature but more mass

200 mL

80ºC

A400 mL

80ºC

B

Thermal energy relationships a. As temperature increases, so does

thermal energy (because the kinetic energy of the particles increased).

b. Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

c. Energy always travels from a high concentration(warm) to a lower concentration(cool) of heat.

Land heats up and cools down faster than water. The temperature of the water helps keep the

land temperature stable.

Specific heat(CH2O) is the amount of heat required to raise the temperature of 1 kg of a material by one degree (C° or K). 1) C(H2O) = 4184 J / kg C° = 4.18 kJ / kg C° 2) C(sand) = 664 J / kg C°This is why land heats up

quickly during the day and cools quickly at night and why

water takes longer.

How to calculate changes in thermal energy

Q = m x T x Cp

Q = quantity of thermal energym = mass of substanceT = change in temperature (Tf – Ti)Cp = specific heat of substance(p)

Heat TransferHow much heat is required to warm

230 g of water from 12°C to 90°C?GIVEN:m = 230 gTi = 12°CTf = 90°CQ = ?C(H2O)= 4.184 J/g·oC

WORK:Q = m·T·Cp

m = 230 gT = 90°C - 12°C = 78°CQ = (230g)(78˚C)(4.184 J/g·oC)Q = 75,061 J

Calorimeters are used to measure the specific heat of a substance. Professional King’s Ridge