Ch 13: Heat and Temperature

• Temperature–measure of the average KE

(motion) of particles (atoms or molecules)–Faster they move…more KE…

higher temperature–Higher temperature…faster they

move…more KE

Thermometers• Thermometers work because the substance

(alcohol if it’s red, mercury if it’s silver) heats up, expands and rises

• 3 temperature scalesoC oF K

• water freezes 0o 32o 273• water boils 100o 212o 373• room temp 22o 72o 295• body temp 37o 98o 310• lowest temp -273o -460o 0

• Kelvin scale is an absolute scale… nothing can go lower than 0K (absolute zero), because at 0K it has no energy…even atoms are frozen

Temperature and Energy Transfer

• Things feel hot or cold because energy is being transferred

• This transfer of energy is called heat. Amount of heat transferred depends on temp. differences.

• Energy flows from high to low concentration, that is from hot to cold things

• Why does ice feel cold?

• Why does a heater feel hot?

• Because heat is leaving your hand

• Because heat is entering your hand

Conduction and Convection

• when objects are in contact with each other, heat flows directly from the hotter one to the colder one. This is conduction.

• fluids (gas or liquid) move and take energy from hotter to colder. This is convection.

• if happens in a cycle due to changing densities, it is called a convection current.

• Both of these only happen when there is matter present (not in a vacuum, like space)

Radiation

• Energy transferred without contact, by electromagnetic waves

(visible light, UV, infrared, microwaves, etc.)

• Only form of heat transfer that does not need matter to happen, but

can happen with matter, too.

• Movie: Comparing Convection, Conduction, and Radiation

Where do you see all three?

Conductors and Insulators• Materials that carry/transfer heat

energy well are called conductors. Most metal objects are good conductors.

• Materials that do not allow heat energy to flow are called insulators. Styrofoam, gasses, wood, plastic and rubber are all good insulators.

• So how does styrofoam keep something both hot and cold?

• It doesn’t “know”…it just doesn’t allow heat to transfer either way…in or out.