Physical Science Chapter 16 Thermal Energy & Heat

Thermal Energy Sometimes called internal energy Depends on the object's mass, temperature, and phase (solid, liquid, gas) TOTAL potential and kinetic energy of all the particles in an object

Heat vs. Temperature Heat Temperature a measure of how hot or cold an object is compared to a reference point A measure of the AVERAGE kinetic energy of the particles in an object The spontaneous flow of THERMAL energy from a hot object to a cold object Change in Energy

Temp, Thermal Energy, & Heat Temperature – a measure of the AVERAGE kinetic energy of the individual particles of a substance. Thermal energy – TOTAL energy of all of the particles Heat – THERMAL energy moving from a warmer object to a cooler object, trying to reach thermodynamic equilibrium.

Thermal energy vs. temp Now remember that thermal energy, unlike temperature, depends on mass Compare a cup of tea and a teapot full of tea, both at the same temperature Is the average kinetic energy the same in both? YES! (that’s why they have the same temperature) Which has more thermal energy and why? The teapot because it has more particles (mass)!

Thermal energy varies with temperature Compare a cup of hot tea with a cup of cold tea Assume each cup is the same size and has the same mass Does each cup have the same amount of particles? Yes Which has the higher average kinetic energy? Hot tea So, which has the greater thermal energy?

Thermal energy Which has more thermal energy? Pitcher of cool lemonade or cup of hot tea? Pot of boiling water or an iceberg? Eureka - Temperature vs. heat

So, how do thermometers work? Thermal expansion and contraction Particles move faster and expand as they warm So, as the temperature increases, the alcohol in the tube expands and its height increases

Absolute zero- that temperature where the individual particles contain no more energy. The particles (atoms and/or molecules) cease vibrating. No movement occurs. 0o Absolute Zero -459o -273o

Warm-up Section 16-1 Review p.478 In which direction does heat flow on its own spontaneously? Name 2 variables that affect the thermal energy of an object. Why is it necessary to have regularly spaced gaps between sections of a concrete sidewalk?

Calorimeter Measures changes in thermal energy Uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature. Read p.478 in textbook

Thermodynamics

Heat Transfer Heat moves in only one direction: from a warmer object to a cooler object Two drinks in the same room: The hot coffee __________ to room temp because . . . The iced tea _______ to room temp because . . .

Hot coffee cools to room temp because the heat of the coffee is transferred to the cooler temperature of the room. A cold glass of Iced tea soon warms up to the surrounding room temperature because the warmer temperature of the room’s surroundings is transferred to the colder glass of iced tea thereby warming it up.

Heat Transfer Specific Heat Video Heat is transferred in one of three ways: Conduction Convection Radiation Specific Heat Video

Heat Transfer Tutorial

Conduction Conduction – heat is transferred from one object to another by direct contact. Examples include: a metal spoon in hot water gets hot or a pot gets hot as it sits on an electric stove. Fastest in solids. Much slower in gases. Why? (think about collisions)

Conductors vs. Insulators Conductor – a material that transfers heat well: metal, tile, glass - high rate of thermal energy transfer Insulator – a material that does not transfer heat well: air, carpet, wood, wool - low rate of thermal energy transfer Conductors vs. Insulators animation Conductors vs. Insulators activity

Why does a tile floor feel colder than a wood floor, even though they're both at room temperature? The tile feels colder because it is a better conductor and transfers thermal energy rapidly away from your skin.

Conduction in different phases -Slower in gases than in liquids and solids because there is more space in between molecules -Dressing in layers to insulate -Gaps of air in layers of blankets, newspapers, etc.

Why does a thick wool sweater keep you warm?

Convection Convection – the transfer of thermal energy when particles of a fluid move from one place to another….the particles transfer the heat. Examples include: a pot of boiling water sets up convection currents to move the hot water at the bottom of the pot being heated to the cooler water at the top of the pot, convection currents in a heated room keep the temperature uniform.

Convection of warm air Air is heated by sunlight The temperature of the air Increases The air Expands The less dense air Rises The denser air Sinks

Radiation Radiation – transfer of energy by electromagnetic waves. Examples include: the Sun’s energy traveling through space and heating up the Earth w/out heating space itself, Heat lamps used at fast food restaurants, and the radiator of a car dissipating the heat of an engine.

Radiation All objects radiate energy: a fire, the sun, your body As temp goes up the rate at which it radiates goes up infrared gallery

What type of heat transfer is represented by each arrow?

Physical Science Hot Body Competition Rules: 1. Must hold ice cube in 1 hand and can't transfer it to the other. 2. No blowing into hand or rubbing with other hand. 3. If cube is dropped you are out. 4. You must melt entire cube.

Laws of Thermodynamics 1st Law- energy is conserved 2nd Law- heat energy can only go from a cold to a hot object if work is done Refrigerator A heat engine converts heat into work One consequence of the 2nd law is that the efficiency of a heat engine is always less than 100% Waste heat must be lost for the heat engine to work!!! 3rd Law- absolute zero can’t be reached

Quick Quiz Review Heat vs. Temperature Thermal Energy Go over Ch. 16.2 Assessment p.483 #1-10, p.496 #28-30