Unit 2: Heat and Energy

What is energy?

• Energy is defined as “the ability to do work”, or, in other words, to make things MOVE.

• Stored energy is called potential energy.

• Moving energy is called kinetic energy.

Can you think of some examples of each around you? Which kind is more common?

KE-PE Conversions• Kinetic Energy (KE) is the name for energy

associated with moving objects. • Potential Energy (PE) is the name for energy

stored in an object--or, the "potential" of an object to do work.

• The picture below of Horseshoe Fall at Niagara Falls illustrates the difference between kinetic and potential energy. In this case, the two forms of energy are experienced by molecules of water. Potential energy (due to gravity) at the top of the waterfall is converted into kinetic energy as is moves down the waterfall.

Elastic Potential

Energy

• One form of potential energy is elastic potential energy. This is the energy stored in elastic materials as the result of their stretching or compressing. (Ex: rubber bands, bungee chords, trampolines, springs, an arrow drawn into a bow, etc).

• The amount of elastic potential energy stored in such a device is related to the amount of stretch of the device - the more stretch, the more stored energy.

Gravitational Potential Energy

• Gravitational potential energy is the energy stored in an object as the result of its height (vertical position).

• The energy is stored as the result of the gravitational attraction of the Earth for the object. The gravitational potential energy of an object is dependent on two variables - the mass of the object and the height to which it is raised.

• The TOTAL energy of the pendulum remains the same (sum of KE and PE), although the pendulum will eventually slow down due to friction with the air.

pendulum

Chemical Potential Energy

• Chemical potential energy is stored in the bonds between atoms in a molecule.

• This energy is released when the bonds are broken in a chemical reaction (Ex: combustion, digestion, etc… )

What happens when energy is added to matter?

• When energy is added to matter it can..

-Make matter move.

-Heat matter up.

Adding energy to matter causes the atoms and molecules that make up the matter to move around. This creates heat (and sometimes light).

Adding energy can also break apart the bonds between atoms and molecules, causing a phase change (solid↔liquid↔gas).

Thermal Energy and Temperature

Heat is the movement of thermal energy from warm objects to cooler objects.

Atoms and molecules will vibrate and move as more and more energy is absorbed.

Temperature is a measure of the average kinetic energy of the moving particles.

How is thermal energy transferred?

• Heat always moves from a warmer place to a cooler place.

This means that…

• Hot objects in a cooler room will cool to room temperature.

• Cold objects in a warmer room will heat up to room temperature.

Practice Questions

• If a cup of coffee and a red popsicle were left on the table in this room what would happen to them? Why?

• ANS: The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature.

Heat transfer occurs in three ways:

• Conduction

• Convection

• Radiation

Conduction

When you heat a metal strip at one end, the heat travels to the other end.

As you heat the metal, the particles vibrate. These vibrations make the adjacent particles vibrate, and so on and so on… the collisions between atoms cause the vibrations to pass along the metal causing heat transfer. This form of heat transfer is conduction.

Heat added

Heat transfer

Why are metals such GOOD CONDUCTORS?Metals have enhanced conductivity!

The outer electrons of metal atoms drift, and are free to move.

When the metal is heated, this ‘sea of electrons’ gain kinetic energy and transfer it quickly throughout the metal.

Insulators, such as wood and plastic, do not have this ‘sea of electrons’ which is why they do not conduct heat as well as metals.

Why does metal feel colder than wood, if they are both at the same temperature?

Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

Convection

What happens to the particles in a liquid or a gas when you heat them?

The particles spread out and become less dense.

This causes fluid to move.

What is a fluid?

A liquid or gas.

Fluid movement

Cooler, more dense fluids sink through warmer, less dense fluids. This means that warmer liquids and gases rise up and cooler fluids sink.

Water movement in a convection current

Hot water rises

Cooler water sinks

Convection current

Cools at the surface

Why is it windy at the seaside?

Cold air sinks

Where is the freezer

compartment put in a fridge?

Freezer compartmen

t

It is put at the top, because cool air sinks, so it cools the food on the way down.

It is warmer at the

bottom, so this warmer

air rises and a

convection current is

set up.

The third method of heat transfer

How does heat energy get from the Sun to the Earth? There are very few

particles between the Sun and the Earth so it CANNOT travel by conduction or by convection.

?RADIATION

Practice Questions

Radiation travels in straight lines

True/False

Radiation can travel through a vacuum

True/False

Radiation requires particles to travel

True/False

Radiation is energy in the form of a wave

True/False

Solar Cookers and Heat Absorption ExperimentsFour containers full of water were placed equidistant from a heat source (ex. the sun). Which container would have the warmest water after ten minutes?

The __________ container would be the warmest after ten minutes because its surface absorbs heat radiation the best. The _________ container would be the coolest because it is the poorest at absorbing heat radiation.

dull black

shiny metal

Shiny metal

Dull metal

Dull black

Shiny black

Practice questions

Why are houses painted white in hot countries?

White reflects heat radiation and keeps the house cooler.

Why can shiny foil blankets be used as emergency blankets to avoid hypothermia?

The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

Why does hot air rise and cold air sink?

Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.

What is electromagnetic radiation?

• Gamma rays • Radio waves

Electromagnetic radiation is energy that travels as electromagnetic waves. The electromagnetic spectrum is the full range of energy waves, from high energy gamma rays to low energy radio waves.

Wavelengths in the Electromagnetic Spectrum

According to the diagram, what type of EM radiation passes through Earth’s

atmosphere? What type gets blocked?

Adding CO2 to the atmosphere increases this arrow! So more heat istrapped by the CO2 that wouldNORMALLY beallowed to escape. In a way, the CO2 acts as a giantblanket!

What is the greenhouse effect?Shortwave visible sunlight passes through the atmosphere to the earth below, but longwave infrared (heat) from the earth does NOT pass through.

How does CO2 cause climate change?

CO2 and other greenhouse gases act like the glass in a greenhouse, allowing short-wave energy to pass through, but trapping long-wave radiation inside. Over time, temperature may rise even further due to positive feedback cycles.

How is energy transferred within the earth?

• Energy from the earth’s core heats the surrounding rock in the mantle.

• Mantle rock melts and rises towards the surface.• This causes volcanoes and results in igneous

rock formation.• Movement of mantle rock also causes tectonic

plate movement and mountain building.• Link to convection demo: http://www.edumedia-sciences.com/a399_l2-

mantle-convection.html

The Rock Cycle

The internal energy of the Earth causes matter to cycle through the solid earth. The rock cycle involves recycling of rock material in convection currents within the mantle layer of the earth. Hot, low density molten rock called magma rises to the surface. Near the surface, magma cools and becomes denser. This denser, cooler rock sinks below once again to complete the cycle.

Review: What is a phase change?

Matter undergoes a phase change when it moves between the solid, liquid or gas states.

There are four examples of phase changes:

1. melting

2. freezing

3. evaporating

4. condensing

NEXT LAB: What is a heating curve?

• A heating curve shows phase changes for a particular substance.

Evaporating

melting

Warming up

How does the water cycle result from solar energy?

The sun causes water to cycle through earth’s major reservoirs through a series of processes involving evaporation, wind, condensation, runoff and groundwater.

Renewable or nonrenewable???

Where does energy come from?• We get energy to power our home

appliances from electrical power plants…. but this energy has been converted from other sources.

• Our energy sources are classified as either renewable or non-renewable, depending on how quickly the source can be replaced.

What are non-renewable energy sources?

• Petroleum, natural gas, and coal are the main sources of energy in use today. All of these fuels are classified as fossil fuels.

Why are they called fossil fuels?• They are all made from decayed plants and animals

that have been preserved in the earth's crust by pressure, bacterial processes and heat. It takes millions of years for these organisms to chemically change into fossil fuels.

• Although these processes are still occurring today, we are using up the fossil fuels MUCH FASTER than they can be replaced.

What is Petroleum?• Liquid fossil fuels, like petroleum, are formed in

areas that geologists believe were once covered by oceans or seas. These fuels were formed when dead plants and animals sank to the bottom of the ocean and were covered by sediments. Over long periods of time (millions of years), the sediments were changed into sedimentary rocks and the plant and animal remains into oil.

• This is an example of a folded-rock

layer oil trap being drilled for

petroleum.

Other fossil fuels

• Another type of fossil fuel is natural gas (methane). It is found sometimes with petroleum, with coal, or by itself. Since it is less dense, it is most often found on top of oil pools. Natural gas is valuable because it burns cleanly, releases energy, and can be easily transported in underground pipelines. We use natural gas in many ways including heating our homes and cooking our food.

• Coal is solid and is formed from pressurized peat, or partially decomposed plant material. There are different varieties of coal which are the result of geologic forces having altered plant material in different ways. Some forms of coal contain a lot of sulfur, which contributes to acid rain.

Fossil Fuels• Burning coal, natural gas, and petroleum releases chemical

energy stored in the fuel. This energy is released as heat when the fuels are burned. The energy contained by the fuels originally comes from the energy of the sun.

• Advantages• Depending on the fuel, relatively easy to obtain • Simple combustion process can directly heat or generate electricity • Inexpensive • Easily distributed to many different areas

• Disadvantages• Produces carbon dioxide and contributes to global warming • Questionable availability of some fuels...major price swings based on

politics of oil regions • Cause of acid rain

Nuclear Fission

Nuclear fission involves the splitting of a heavy element into lighter elements. The reaction is set off by a neutron shooting into an atom’s nucleus. In this reaction, matter is transformed into energy in a process that is several million times as energetic as combustion (chemical burning).

• Advantages• Relatively little fuel is needed and the fuel is relatively inexpensive and

available in trace amounts around the world. • Fission is not believed to contribute to global warming or other pollution

effects associated with fossil fuel combustion

• Disadvantages• Possibility of nuclear meltdown from uncontrolled reaction--leads to nuclear

fallout with potentially harmful effects on civilians • Waste products can be used to manufacture weapons • High building cost because plant requires containment safeguards

Chernobyl

Hydroelectric • Hydroelectric systems make use of the energy in running water to create

electricity. In coal and natural gas systems, a fossil fuel is burned to heat water. The steam pressure from the boiling water turns "propellors" called turbines. These turbines spin coils of wire between magnets to produce electricity. Hydropowered systems also make use of turbines to generate electrical power; however, they do so by using the energy in moving water to spin the turbines.

• Advantages• Unlimited fuel source • Minimal environmental impact • Produces high levels of energy• Can be used throughout the world

• Disadvantages• Smaller models depend on availability of fast flowing streams or rivers • Run-of-the-River plants can impact the mobility of fish and other riverlife.

NOTE: Building a fish ladder can lessen this negative aspect of hydroelectric power

Biomass• Biomass is energy produced from organic substances.

The key to the power of biomass lies in the energy of the sun. All plants undergo a process called photosynthesis, whereby the plants use chlorophyll to convert the energy in the sun's rays into stored energy in the plants. This is released when the organic substances are burned.

• Advantages• (Theoretically) unlimited fuel source • Alcohols and other fuels produced by biomass are efficient,

viable, and relatively clean-burning • Available throughout the world

• Disadvantages• Could contribute a great deal to global warming and particulate

pollution if directly burned • Still an expensive source, both in terms of producing the

biomass and converting it to alcohols

Solar Power• The energy of the sun can be used in many ways. When plants grow, they

store the energy of the sun. Then, when we burn those plants, the energy is released in the form of heat. This is an example of indirect use of solar energy.

• The form we are interested in is directly converting the sun's rays into a usable energy source: electricity. This is accomplished through the use of "solar collectors," or, as they are more commonly known as, "solar panels."

• Advantages• Unlimited fuel source • No pollution • An excellent supplement to other renewable sources • Versatile--is used for powering items as diverse as solar cars and satellites

• Disadvantages• Low energy production--large numbers of solar panels (and thus large land

areas) are required to produce useful amounts of heat or electricity • Only areas of the world with lots of sunlight are suitable for solar power

generation

Wind• Differences in air pressure due to differences in temperature are the main

cause of wind. Because warm air rises, when air masses of different temperatures come in contact, the warmer air rises over the colder air, causing the wind to blow.

• Wind generators take advantage of the power of wind. Long blades, or "rotors", catch the wind and spin. Like in hydroelectric systems, the spinning movement is transformed into electrical energy by a generator.

• Advantages• Unlimited fuel source • No pollution • An excellent supplement to other renewable sources • Disadvantages• Low energy production--large numbers of wind generators (and therefore

large land areas) are required to produce useful amounts of heat or electricity

• Only areas of the world with lots of wind are suitable for wind power generation

• Relatively expensive to maintain; it does not generate very much energy for the price.

GeothermalThe earth's crust is heated by the decay of radioactive elements. The heat is carried by magma or water beneath the earth's surface. Some of the heat reaches the surface and manifests itself in geysers and hot springs throughout the world.Geothermal power can be used to directly heat buildings. The pressurized steam from superhot water beneath the earth's surface can be used to power turbines and generate electricity.

•Advantages•Unlimited energy source •No pollution •Can be directly used to heat or produce electricity (very cheap) •An excellent supplement to other renewable sources

•Disadvantages•Not available in many locations •Not much power per vent

World energy use • This graph indicates the role of

various energy sources in world

electricity generation. Which

is the greatest source of energy? • Note that hydroelectric has a slightly larger share

of world electricity generation than nuclear, whereas in the United States it is opposite.

• This is due to the fact that many other countries can use hydroelectric power more easily than the US because of less populated cities.

How is heat used to generate electricity?• Most of the electricity in the united

states is produced using steam turbines.

• A turbine converts kinetic energy from a moving fluid (liquid or gas) to mechanical energy.

• Heat from a fuel source such as nuclear power, coal burning, is used to create steam, which is then used to spin the blades on a turbine.

• A turbine that spins in a magnetic field will generate electricity.

What are the different forms of Energy?

Energy appears in many forms. There are five main forms of energy.

• Mechanical –energy associated with motion

• Heat (thermal) –energy of vibrating molecules

• Chemical –energy of chemical bonds

• Electromagnetic (radiant) –energy that travels in waves (such as electricity, light, UV, radio)

• Nuclear –energy from the nucleus of an atom

If we get most of our energy from the sun, then where does the sun

get IT’S energy?

• Nuclear reactions (fusion) occurs in the sun. This cannot be easily reproduced on Earth because VERY high temperatures and pressures are required.

Energy cannot be created or destroyed… however, energy can

be converted from one form to another.

• Energy enters the Earth system primarily as solar radiation, it is captured by materials and photosynthetic processes, and is eventually transformed into heat… How does this work?

Energy transformations• Some forms of energy can be converted to other forms.

• For example, solar panels are used to capture light energy from the sun and convert it to electricity.

• Green plants undergo photosynthesis to convert light energy into chemical energy in the form of food.

• The mechanical energy of a waterfall can be converted to electromagnetic

energy in a generator. Generators convert other types of mechanical energy into electromagnetic energy.

Examples of Energy Conversions

• Photosynthesis is the process by which plants are able to

capture light energy and use that energy to make glucose. In this process sunlight provides the energy needed by chlorophyll to change molecules of carbon dioxide and water into glucose (a type of sugar). Chemical energy is stored in the plants.

• FOOD: When a cow eats a plant, the chemical energy stored in the plant is transferred to the cow, which can be converted into mechanical energy. The cow also uses the energy to make muscle (beef). This energy is then transferred to you as you eat your hamburger.

• COMBUSTION: Plants, such as wood, can also be burned to convert the stored chemical energy into heat and light (electromagnetic) energy).

Energy Conversions

• It usually takes a whole series of energy conversions to do a certain job. For example, just to get the energy to make a piece of toast, there are several energy conversions involved. What are they?

chemical → electrical → heat• How does this work?• Chemical energy stored in coal is released as heat and

light energy when the coal is burned. The heat energy is used to produce steam and is changed into mechanical energy in a generator. The generator converts mechanical energy into electric energy that travels through power lines into your home. When you use your toaster, that electric energy is again changed into heat energy.

More Examples of Energy Conversions

• Rubbing your hands together… chemical → mechanical → heat• Coal burning in a grill

chemical → heat + radiant• Power generated at a hydroelectric plant

mechanical → electromagnetic• Baking cookies

electromagnetic → chemical + heat

Conservation of Energy• Have you ever touched a lightbulb when it was on?

Or tried to change it when it burnt out after being on? What you have discovered is the conversion process of energy!

• When you turn on a light, not all of the electricity is converted to light energy. Some of the energy is converted to heat.

• Although some energy is changed to heat and does not help do the work, the energy is not lost. In fact, energy is never lost; it is only converted from one form to another. This is stated in the law of conservation of energy, energy can not be created nor destroyed by ordinary means.

THE END

Hydrothermal Vents

Angler fish

Some Review Topics

• What happens when heat is added to matter?• What is a “phase change”? What does it mean?• How is heat energy transferred?• Describe how is energy transformed (or

converted) from one form to another using heat, light, electricity and motion as examples.

• Explain how solar energy causes water to cycle through major earth reservoirs.

• Explain how internal energy of the earth causes matter to cycle through the solid earth.

Some Review Topics

• How is heat used to generate electricity?• What are some advantages and disadvantages

to using fossil fuels and nuclear fuel? What environmental issues are associated with these fuels?

• What are some advantages and disadvantages to using wind, solar and hydroelectric energy? What environmental issues are associated with these sources?

• Discuss why alternative energy sources being explored and used to address the disadvantages of using fossil and nuclear fuels.