heat and heat technology

Heat and Heat Technology

Section 1 Temperature

Essential Questions

• Describe how temperature relates to kinetic energy.• Compare temperatures on different

temperature scales.• Give examples of thermal

expansion.

What is Temperature?

• Temperature is a measure of kinetic energy.• Kinetic energy is the energy of motion.

All moving objects have kinetic energy. • Kinetic energy of an object depends on

the object’s mass and speed.

Temperature and Kinetic Energy

• All matter is made of atoms or molecules that are always moving.• The faster the particles move, the more

kinetic energy they have. • The more kinetic energy an object has,

the higher the temperature of the object.

• The gas particles on the right have more kinetic energy than those on the left. So, the gas on the right is at a higher temperature.

Average Kinetic Energy of Particles

• Motion in matter is random, so each particle has a different amount of kinetic energy.• An object’s temperature is the average

kinetic energy of the particles in the object.

Measuring Temperature• Thermometers can measure temperature

because of thermal expansion.• Thermal expansion means that when a

substance’s temperature increases, its particles move faster and spread out – creating more volume (expansion).

Temperature Scales• The Celsius scale is the most widely used

temperature scale.• The Fahrenheit scale is the one we use in

the US.• The Kelvin scale is the official SI

temperature scale.–The lowest temperature on the Kelvin scale

is 0 K, which is called absolute zero.

Temperature Conversions

• Temperature is represented by different numbers on the three temperature scales.

Copy and study this chart

More About Thermal Expansion• Expansion Joints on Highways –Hot weather can make a bridge expand as

the bridge expands, it is in danger of breaking.

• Expansion joints keep segments of the bridge apart so that they have room to expand without the bridge breaking.

• Bimetallic Strips in Thermostats are made of two metals stacked in thin strips. The metals expand at different rates, a strip coils and uncoils in response to changes in temperature, as shown below.

Heat and Heat Technology

Section 2 What is Heat?

Essential Questions

• Define heat as thermal energy transferred between objects at different temperatures.• Compare conduction, convection,

and radiation.• Use specific heat capacity to

calculate heat.

Transferred Thermal Energy

• Heat is the energy transferred between objects that are at different temperatures.• Energy is always transferred from the

object that has the higher temperature to the object that has the lower temperature.

Heat and Thermal Energy• Heat is transferred in the form of thermal

energy. –Thermal energy - total kinetic energy of a

substance. • Thermal energy depends on temperature

and on how much of a substance there is.

Thermal Equilibrium

• Thermal Equilibrium – when objects that are touching reach the same temperature• When objects are at thermal

equilibrium no net change in the thermal energy of either one occurs.

Conduction• Thermal Conduction - transfer of

thermal energy through direct contact.–Conduction can also occur within a

substance.• When particles of a substance touch,

kinetic energy is transferred until the energy (and temperature) is even throughout.

Conductors and Insulators

• Thermal conductors – substances that conduct heat well–Ex: most metals

• Thermal insulators – substances that do NOT conduct heat well–Ex: wood and plastic

Convection

• Convection - transfer of thermal energy by the movement of a liquid or a gas.–Takes place because of density–Warmer liquids rise, then begin to cool

back down–Cooler liquid sinks and then begins to

warm back up–The cycle repeats

Radiation

• Radiation - transfer of energy by electromagnetic (EM) waves. –All objects radiate EM waves.

• Radiation can involve either a transfer of energy between particles of matter OR an energy transfer across empty space.–Ex: warmth of the sun

• Radiation and the Greenhouse Effect–Earth’s atmosphere allows the sun’s visible

light to pass through it. –The atmosphere also traps energy within

its’ gases, too.• This process is called the greenhouse

effect. Without it, Earth would be a cold, lifeless planet.• Global warming concern: if too much

energy is trapped in the atmosphere, the Earth may become too warm

Specific Heat

• Specific Heat - energy needed to change the temperature of 1 kg of a substance by 1°C. –Higher the specific heat, the more energy it

needs to increase its temperature.• Most metals have lower specific heats.• Specific heat of water is very high.

Calculating Heat• heat (J) specific heat (J/kg•°C) mass (kg)

change in temperature (°C) • Calculating Heat - When the temperature

increases, the value of heat is positive. • When the temperature decreases, the value of

heat is negative.

Heat and Heat Technology

Section 3 Matter and Heat

• Identify the three states of matter. • Explain how heat affects matter

during a change of state.• Describe how heat affects matter

during a chemical change.• Explain what a calorimeter is used

for.

Essential Questions

• State of matter - the physical forms a substance –solid, liquid, and gas (and plasma)

• The state of a substance depends on the speed of its particles, the attraction between them, and the pressure around them.

States of Matter

• Changes of State are physical changes – changes from one state to another• Changes of state include freezing

(liquid to a solid), melting (solid to liquid), boiling and evaporation (liquid to gas), condensation (gas to liquid), and sublimation (solid to gas).

Changes of State

• Temperature is the SAME during a change of state, whether the temperature is increasing or decreasing

Copy and study the graph

• Heat is also involved in chemical changes • During a chemical change, a new

substance is formed. –Sometimes a chemical change requires heat• Ex: baking a cake

–Sometimes a change releases energy in the form of heat• Ex: wood burning

Heat and Chemical Changes

• Food and Chemical Energy –Food gives your body energy.–Energy is released in a chemical reaction

when compounds such as carbohydrates are broken down in your body.

• The energy is released in chemical reactions. • Calorie – unit used to measure the

amount of energy in food

• Calorimeters - a device that measures heat. The energy lost by one object is gained by the other object through thermal energy.

Heat and Heat Technology

Section 4 - Heat Technology

• Analyze several kinds of heating systems.• Describe how a heat engine works.• Explain how a refrigerator keeps food

cold.• List some effects of heat technology on

the environment.

Essential Questions

• Hot–Water Heating - the high specific heat of water makes it useful for heating systems.

Heating Systems

Warm–Air Heating •Air cannot hold as much energy as water can.

•Warm–air heating systems are used in many homes & offices in the U. S.

• Heating and Insulation –Insulation reduces the transfer of

thermal energy. –Insulation is used buildings so less

heat passes into or out of the building.• Solar Heating systems use the sun’s

energy to heat houses and buildings.

• Heat engine - a machine that transforms heat into mechanical energy, or work.• Combustion – how heat engines use fuel• External Combustion Engines – burns

fuel outside the engine–Ex: steam engine

Heat Engine

• Internal Combustion Engines – burns fuel inside an engine–Ex: car engine–Fuel (gas) is burned inside the engine,

inside the cylinders. –The cylinders go through a series of steps

to burn the fuel.

Cooling Systems• Cooling systems move heat OUT of an area• Cooling and Energy - The compressor does

the work of cooling by compressing the refrigerant. The refrigerant is a gas that has a boiling point below room temperature, which allows it to condense easily.

Heat Technology and Thermal Pollution

• A negative effect of thermal energy is thermal pollution, the excessive heating of a body of water.

• Thermal pollution can happen near large power plants, which are often located near a body of water–It can effect the ecosystem in the area