NATS 101 Updates Add your name to Class ListServe! Still missing 100 students First Quiz next Thursday Practice Quiz today

Turn off clickers

Turn on clickers

Lecture 3 Temperature, Heat Transfer NATS 101 Lecture 3 Temperature, Heat Transfer

What is Temperature? Microscopic View Energy due to random jiggling of molecules Related to average molecular speed; 500 m/s (=1100 mph) at room temperature for air

Temperature and Density Consider volume of air If air is warmed: The molecules will move faster, have “stronger” collisions, and tend to become spaced farther apart Volume increases, so density decreases Warmer  less dense

Temperature Scales Fahrenheit (oF) - relative US public standard Celsius (oC) - relative Freezing point 0oC Boiling point 100oC oC = 5/9 (oF-32) oF = (oC 9/5) + 32 Kelvin (K) - absolute K= oC+273 Ahrens p27

What is Heat? Heat-Energy in the process of being transferred from a warmer object to a cooler object Consider a pot of water on a hot burner. Consider the following questions: Williams, p. 19

Heat Transfer Questions What causes the… Pan bottom and handle to get warmer? Top of the water to become warmer? Water temperature to not exceed 100oC? Region away from side of pan to feel warm? Williams, p. 19

Conduction Heat transfer due to collision of molecules. Conduction warms the bottom of the pan! Conductivity - rate of heat transfer across a 1 cm thick slab of material if one side is kept 1oC warmer than the other Cheap Experiment: Touch your chair! 1 cm Metal Water Air Heat Transfer 1oC 0oC

Heat Conductivity

heat below - convection heat top - no convection Heat transfer due to vertical exchange of mass Occurs in fluids (liquids, gases) because of gravity Warm, buoyant air rises - Cool, dense air sinks Convection warms top of liquid! Warm Cool heat below - convection heat side - convection heat top - no convection gravity

Convection Movies 2D Convection Tank Animation  3D Rayleigh-Benard Convection Model  Last hour movie of clouds and moist convection over Catalina mountains

Energy States and Water Phases water molecules are tightly packed in a crystal alignment that prevents them from changing shape LOW ENERGY STATE attractive forces btw molecules weaken and individual molecules can move around each other, but they can not break away SLIGHTLY HIGHER ENERGY STATE water molecules move very rapidly and are not bound together EXTEMELY HIGH ENERGY STATE Large Energy Change Small Energy Change

Strong attraction between molecules Weak attraction between molecules Latent Heat Surrounding air cools Less Ordered Phase More Ordered Phase -620 cal/gm Strong attraction between molecules -80 cal/gm -540 cal/gm Weak attraction between molecules Some attraction +80 cal/gm +540 cal/gm +620 cal/gm Surrounding air warms Ahrens, p 28

Energy Transfer The explosive TNT--trinitrotoluene-- releases 3,800 calories per gram, roughly 6 times that per gram of water latent heat. Its energy release may be extremely sudden, but per unit weight, TNT contains less energy than sugar. Latent Heat Williams, p. 19

Heat Transfer Questions What causes the… Pan bottom and handle to get warmer? Top of the water to become warmer? Water temperature to not exceed 100oC? Region away from side of pan to feel warm? Williams, p. 19

Modes of Heat Transfer Latent Heat Williams, p. 19

Take Home Concepts Heat-Energy transfer due to temperature differences Three modes of heat transfer Conduction – molecule to molecule Convection – transport of fluid Radiation – electromagnetic waves Latent Heat – energy of phase changes