Chapter 6: Thermal Energy. Section 1: Temperature and Heat Temperature is related to the average kinetic energy of the particles in a substance.

Chapter 6: Thermal Energy

Section 1: Temperature and Heat Temperature is related to the average

kinetic energy of the particles in a substance.

Temperature Continued… SI unit for temp. is the Kelvin

K = C + 273 (10 ºC = 283 K) C = K – 273 (10 K = -263 ºC)

Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.

Thermal Energy Relationships As temperature increases, so does thermal

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

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).

Heat Heat- The flow of

thermal energy from one object to another.• Heat always flows from

warmer to cooler objects.

Cup gets cooler while hand gets

warmer

Ice gets warmer while

hand gets cooler

Specific Heat Some things heat up or cool down faster

than others.

Land heats up and cools down more quickly than water.

Where Would You Rather Sit On a Hot Sunny Day?

Specific Heat Continued… Specific heat is the amount of heat

required to raise the temperature of 1 kg of a material by one degree (C or K). Specific heat (C) water = 4184 J/kg ºC Specific heat (C) sand = 664 J/kg ºC

This is why land heats up quickly during the day and

cools quickly at night and why water takes longer.

Why Does Water Have a High Specific Heat???

water metal

Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds

and do not need as much energy to break them.

Calculating Changes In Thermal Energy Q = m x T x C

Q = change in thermal energy (J) m = mass of substance (kg) T = change in temperature (°C)

(Tf – Ti) C = specific heat of substance (J/kg°C)

Lets Do an Example: The air in a living room has a mass of 60.0

kg and a specific heat of 1,020.0J/(kg °C). What is the change in thermal energy of the air when it warms from 20˚C to 25˚C?

Q = m x t x C Q = 60.0 kg x (25˚C - 20˚C ) x 1,020.0J/kg ·˚C Q = 306,000 J

Calorimeter A calorimeter is used to help measure the

specific heat of a substance.

Section 2: Transferring Thermal Energy

Conduction Conduction is the transfer of thermal

energy by collisions between particles in matter. Conduction occurs because particles in matter

are in constant motion. Example: The metal stick that the marshmallows are

on heats up as it is near the flames. The thermal energyis transferred up the metalstick.

Convection Convection is the transfer of thermal

energy in a fluid by the movement of warmer and cooler fluid from place to place. More energetic particles

collide with less energetic particles and transfer thermal energy.

Radiation Radiation is the transfer of energy by

electromagnetic waves. These waves can travel through space even when no matter is present. Example: Sun’s radiation warms Earth Example: When you

sit near a fire, radiant energy warms you.

Radiation Continued…• When radiation

strikes a material, some of the energy is absorbed, some is reflected, and some may be transmitted through the material.

Controlling Heat Flow• Almost all living things

have special features that help them control the flow of heat.

• For example, the Antarctic fur seal’s thick coat helps keep it from losing heat. This helps them survive in a climate in which the temperature is often below freezing.

Controlling Heat Flow Continued… In the desert the scaly skin of the desert

spiny lizard has just the opposite effect. It reflects the Sun’s rays and keeps the

animal from becoming too hot.

Insulators A material in which

heat flows slowly is an insulator. Examples: wood, some

plastics, fiberglass, and air.

Materials like metals that are good conductors are poor insulators.

Reducing Heat Flow A thermos bottle uses a

vacuum and reflective surfaces to reduce the flow of heat into and out of the bottle. The vacuum prevents heat flow by conduction and convection. The reflective surfaces reduce the heat transfer by radiation.

Section 3: Using Heat

Heating Systems Forced-Air Systems

Air heated in a furnace and blows through pipes to individual rooms to heat a home.

Radiator Systems Closed metal container that

contains water or steam. Thermal energy is transferred to surroundings by conduction, then by convection.

Electric Heating Systems No central furnace. Electrically

heated coils placed in floors and walls. Heat moves through room by convection.

Solar Heating Passive Solar Heating

Radiant energy from the sun is transferred to the room through windows.

Active Solar Heating Uses solar collectors to absorb solar energy

which heats water in pipes. A pump circulates the water to radiators throughout the house.

Thermodynamics Thermodynamics- the study of how heat,

thermal energy, and work are related. First Law of Thermodynamics: the temperature

of a system can be increased by adding heat to the system, doing work to the system, or both.

Example: rubbing your hands together to make them warm

Second Law of Thermodynamics: it is impossible for heat to flow from a cool object to a warm object unless work is done.

Converting Heat to Work Heat engine- a device that converts heat

to work. It is impossible to build a device that converts

heat completely into work! Example: A car’s engine converts chemical energy in

gasoline to heat, then the engine transforms some of the thermal energy into work by rotating the car’s wheels.

Only about 25% of the heat released by burning gasoline is converted into work. The rest is transferred to the engine’s surroundings.

Heat Movers A refrigerator

does work on the coolant in order to transfer heat from inside the refrigerator to the warmer air outside.