# Thermal Energy & Heat. Temperature Measure of how hot or cold something is compared to reference point Units: –Celsius –Fahrenheit –Kelvin.

## Presentation on theme: "Thermal Energy & Heat. Temperature Measure of how hot or cold something is compared to reference point Units: –Celsius –Fahrenheit –Kelvin."— Presentation transcript:

Thermal Energy & Heat

Temperature Measure of how hot or cold something is compared to reference point Units: –Celsius –Fahrenheit –Kelvin

Temperature Related to kinetic energy of particles in an object Temp. increases = particles move faster = higher KE Viewing temperature & KE

Thermal Energy Total Potential and Kinetic energy of all particles in an object TE depends on: 1. Mass (# of particles) –Larger mass = higher TE 2. Temperature –Higher temp. = higher TE 3. Phase of object (solid, liquid, gas)

Heat Transfer of thermal energy between objects because of a temperature difference Heat Always flows spontaneously from Hot to cold!

Iron ball at 300 degrees C Container at 50 degrees C. What is the direction of heat flow to cool the iron ball?

Heat Flow Hot soup placed in the fridge. How does it cool? –Heat flows from the soup to the fridge

3 Methods of Heat Transfer 1.Conduction: transfer of heat by direct contact of particles Ex: touching a hot candle

Thermal Conductors materials that conduct heat well Solids (Metals) are best thermal conductors –Particles close together

Thermal Insulator Materials that conduct heat poorly Air, wood, plastic are good insulators Fiberglass Insulation Wood spoon Styrofoam

Methods of Heat transfer (cont.) 2. Convection: Transfer of heat in a fluid caused by differences in density –Heat moves in currents –Fluid = liquid or gas Ex: Hot air/water rises, cool air/water sinks

Methods of Heat Transfer (cont.) 3. Radiation: Transfer of heat by waves (infrared) moving through space –All object’s radiate heat Ex: Sun warming your skin

Comparing Methods Conduction & Convection require matter to transfer heat Radiation does not require matter for heat transfer –Heat from sun travels through outer space

Specific Heat Amount of heat needed to raise the temperature of 1g of a material by 1 °C Materials heat up at different rates Units are J/g °C

Specific Heat Materials with high specific heat take longer to heat up –lots of energy needed Water has high specific heat

Specific Heat Materials with low specific heat heat up faster (little energy needed) Ex: Silver

Calculating Specific Heat Q = m ΔT c Q = heat absorbed in joules m = mass in grams ΔT = change in temperature in °C c = specific heat of material J/g °C Specific heat of copper

States of Matter 1. Solids 2. Liquids 3. Gases

Solids Have definite shape & volume Atoms packed tightly together Vibrate-do not “flow”

Liquids Have definite volume, but NOT definite shape-take shape of container Atoms close together, but CAN flow Putting energy (heat) into a solid can change it to a liquid

Gas Have NO definite shape OR volume-take shape of container Atoms move quickly Adding energy (heat) to liquids (water) can change it to a gas

Phase changes Melting, freezing, vaporization, condensation (all physical changes & reversible) Temp. of a substance does NOT change during phase changeTemp. of a substance does NOT change during phase change Energy is absorbed or released

Vaporization Liquid  gas –Evaporation: takes place @ surface of liquid –Boiling: takes place below the surface of liquid

Condensation Gas  Liquid

Thermal Expansion Thermal Expansion: increase in volume of a material when it is heated (expands) Ex: liquid rising in thermometer

Thermal Contraction Thermal Contraction: decrease in volume of a material when it is cooled (contracts) Ex: balloon shrinks when cooled

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