thermal energy internal energy: energy of the moving particles that compose matter

Thermal Energy

Internal energy: energy of the moving particles that compose matter

Starter 3 Thermal Energy Transfer

• Read Ch. 22.1-22.3• Fold a piece of notebook paper to form three

columns– Head each column with one of the three ways that

thermal energy can be transferred– Define each– List three main points from the reading for each

thermal energy transfer process

• On the back of the paper, prepare an example illustrating how each transfers heat

Today’s Key Terms and Ideas

• Thermal Energy

• Kinetic Theory

• Heat

• Thermal Equilibrium and heat transfer

• Kinetic Theory as it relates to expansion and contraction

• Hot vs. cold

Physics and Particles

• Particle is a general term used to describe molecules, atoms and sub-atomic particles

The higher the temperature of a substance, the faster the motion of its molecules.

This is also referred to as the Kinetic Theory—

a) all matter is made of atoms and molecules that are moving.

b) The higher the temperature, the faster the particles move.

c) Given the same temperature, heavier particles move slower than lighter particles.

21.1 Temperature

Increasing Avg. KE

Increasing Temp.

solid

liquid

gas

Particle speed is increasing

Matter is changing state

melting

evaporation

condensation

freezing

Temperature and Kinetic Energy

Temperature is related to the average kinetic energy of the atoms and molecules in a substance.

The faster the molecules move, the ______________ the temperature and the _____________ the average kinetic energy and the __________ the particle speed.

21.1 Temperature

greater

greater

greater

1. Heat is the quantity of thermal energy transferred

2. Heat always flows from a substance with a higher temperature to a substance with a lower temperature.

3. Heat flows only when there is a difference in temperature.

4. Heat units are calories or joules.

21.2 Heat

Just as water will not flow uphill by itself, regardless of the relative amounts of water in the reservoirs, heat will not flow from a cooler substance into a hotter substance by itself.

21.2 Heat hotter

colder

Entropy!

Flow from higher to lower energy state.

What causes heat to flow?

21.2 Heat

A difference in temperature between objects in thermal contact.

When a substance takes in or gives off heat, its internal energy changes.

21.4 Internal Energy

• Heat flows between two objects of different temperature until they have the same temperature.

• The loss of thermal energy from the warmer object equals the gain of thermal energy for the cooler object

21.3 Thermal Equilibrium

What happens when a warmer substance comes in contact with a cooler substance?

Most forms of matter—solids, liquids, and gases—expand when they are heated and contract when they are cooled.

21.8 Thermal Expansion

When the temperature of a substance is increased, its molecules jiggle faster and normally tend to move farther apart.

This results in an expansion of the substance.• Gases generally expand or contract much

more than liquids.• Liquids generally expand or contract more

than solids.

21.8 Thermal Expansion

Starter Question #2How does a thermometer work?

The kinetic theory be used to explain expansion and contraction of materials when the temperature of the material changes.

As the temperature rises, heat is transferred from the surroundings to the liquid inside the thermometer and the molecules that compose the liquid vibrate faster. This causes the liquid to expand and rise.

As the temperature falls, heat is transferred away from the liquid inside to the surroundings and the molecules that compose this liquid slow down. This causes the liquid to contract.

• The liquid in the thermometer stops rising or falling when thermal equilibrium is reached (no more heat flow!)

Air temperature = Liquid temperature

Do copper, clay and water have the same chemical composition?•No. Copper is composed of Cu atoms and water is composed of H2O molecules. Clay is a complex silicate.•The difference in chemical composition influences how copper, clay and water respond when heat is transferred.

21.6 Specific Heat Capacity

The specific heat capacity of a substance is the quantity of heat required to raise 1 g of a substance by 1 degree Celsius.

A substance with a high specific heat capacity can absorb a large quantity of heat before it will raise in temperature (water has a high specific heat).

A substance with a low specific heat requires relatively little heat to raise its temperature (copper has a low specific heat).

21.6 Specific Heat Capacity

21.6 Specific Heat Capacity

highest

lowest

think!Which has a higher specific heat capacity—water or sand? Explain.

21.6 Specific Heat Capacity

think!Which has a higher specific heat capacity—water or sand? Explain.

Answer:

Water has a greater heat capacity than sand. Water is much slower to warm in the hot sun and slower to cool at night. Sand’s low heat capacity, shown by how quickly it warms in the morning and how quickly it cools at night, affects local climates.

21.6 Specific Heat Capacity

Good conductors have a low specific heat capacity!

A gram of water requires 1 calorie of energy to raise the temperature 1°C.

It takes only about one eighth as much energy to raise the temperature of a gram of iron by the same amount.

21.6 Specific Heat Capacity

The capacity of a substance to store heat depends on its chemical composition.

21.6 Specific Heat Capacity

6. What is the difference between a substance with a high specific heat and a low specific heat capacity?

• Substances with a low specific heat (e.g., metals) need very little heat to raise temperature– Good conductors, not good absorbers, do not

hold onto heat well

• Substances with a high specific heat need a large quantity of heat to raise temperature.– Poor conductors, good absorbers, store and

hold onto heat well

7. How does the specific heat of water help to moderate climate?

• During the summer, surrounding air is cooled by the water and keeps the coast cooler than the intercontinental locations.

• During the winter, the surrounding air is warmed by the water and keeps the coast warmer than the intercontinental locations.

The property of water to resist changes in temperature improves the climate in many places.

21.7 The High Specific Heat Capacity of Water

Water has a high specific heat and is transparent, so it takes more energy to heat up than land does.

21.7 The High Specific Heat Capacity of Water

Water’s capacity to store heat affects the global climate.

Water stores and hold heat well because of its high specific heat.

21.7 The High Specific Heat Capacity of Water

•Gulf Stream brings warm water northeast from the Caribbean. •It holds much of its thermal energy long enough to reach the North Atlantic off the coast of Europe. •As it cools, the energy released is carried by the prevailing westerly winds over the European continent.

The Gulf Stream brings warm winters to Ireland and the prevailing winds off the Atlantic carry with them rain. It means grass can grow almost all year round — creating the lush sweeping pastures of the Emerald Isle. Today they make up 93 percent of all farmland. No other country in Europe has quite as much grass as Ireland.

Climate of Europe

Look at a world globe and notice the high latitude of Europe.

Both Europe and Canada get about the same amount of the sun’s energy per square kilometer.

21.7 The High Specific Heat Capacity of Water

http://www.sampleireland.com/weather-in-ireland-year-round.html

Cork

Edmonton

Same insolation angle, different climate due to proximity to water and the warming effect from the Gulf Stream

Continental Climate

Marine Climate

Climate of America

On the west coast, air moves from the Pacific Ocean to the land.

• In winter, the water warms the air that moves over it and warms the western coastal regions of North America.

• In summer, the water cools the air and the western coastal regions are cooled.

21.7 The High Specific Heat Capacity of Water

The central interior of a large continent usually experiences extremes of temperature.

Land, with a lower specific heat capacity, gets hot in summer but cools rapidly in winter.

8. In which three ways can the thermal energy (or heat) of a substance be transferred?

Heat can be transferred by conduction, by convection, and by radiation.

In conduction, collisions between particles transfer thermal energy, without any overall transfer of matter.

22.1 Conduction

Heat from the flame causes atoms and free electrons in the end of the metal to move faster and jostle against others. The energy of vibrating atoms increases along the length of the rod.

22.1 Conduction

In convection, heat is transferred by movement of the hotter substance from one place to another.

22.2 Convection

Convection occurs in all fluids.

a. Convection currents transfer heat in air.

22.2 Convection

Hot, less dense fluid rises in the presence of cooler, more dense fluid.

Convection occurs in all fluids.

a. Convection currents transfer heat in air.

b. Convection currents transfer heat in liquid.

22.2 Convection

When fluid particles at the bottom of the pan begin to vibrate faster, they expand and decrease in density, making the hotter fluid more buoyant.

In radiation, heat is transmitted in the form of radiant energy, or electromagnetic waves.

22.3 Radiation

Most of the heat from a fireplace goes up the chimney by convection. The heat that warms us comes to us by radiation.

22.3 Radiation

• Radiation is caused by moving electrons or charged particles in matter. The faster the particles move, the higher the frequency of the electromagnetic radiation.

a. Radio waves send signals through the air.

22.3 Radiation

a. Radio waves send signals through the air.

b. You feel infrared waves as heat.

22.3 Radiation

a. Radio waves send signals through the air.

b. You feel infrared waves as heat.

c. A visible form of radiant energy is light waves.

22.3 Radiation

11. What happens to the frequency of radiant energy as the temperature of the substance increases or decreases?

• The frequency of radiant energy increases as the temperature of the substance increases.

http://mail.jsd.k12.ca.us/bf/bflibrary/images/electromagnetic-spectrum.jpg