4-Jun-16 Physics 1 (Garcia) SJSU Chapter 21 Temperature, Heat & Thermal Expansion Part III: Heat

4-Jun-16 Physics 1 (Garcia) SJSU Temperature Temperature of an object indicates average internal energy (due to molecular motion) of the object. Temperature Scales

4-Jun-16 Physics 1 (Garcia) SJSU Heat Transfer Heat always flows from high temperature objects to low temperature objects. Heat flow stops when temperatures equal. Various ways by which heat may flow. 98º 32º 75º Heat flows from child and air into the ice cream Heat flows from child into air

Temperature Conversions To convert between Celsius and Fahrenheit temperatures, use the following equation F=9/5C + 32 C=(F-32)*5/9 To Convert between Celsius and Kelvin temperatures, use the following K=C+273 C=K Jun-16 Physics 1 (Garcia) SJSU

4-Jun-16 Physics 1 (Garcia) SJSU Total versus Average The total amount of money in this room is probably around $1000. The average amount of money per person is probably around $20. Temperature of an object depends on the average amount of energy per molecule, not the total. Bucket of warm water can have more internal energy than cup of hot water. 80 °F 100 °F

4-Jun-16 Physics 1 (Garcia) SJSU Internal Energy Internal energy of an object depends on: Temperature Mass Material 1 kg TemperatureInternal Energy 300 K120,000 J 200 K80,000 J 100 K40,000 J 0 K0 Joules Iron TemperatureInternal Energy 300 K120 J 200 K80 J 100 K40 J 0 K0 Joules Iron 1 gram TemperatureInternal Energy 300 K1,200,000 J 200 K800,000 J 100 K400,000 J 0 K0 Joules Water 1 kg 1000 grams

4-Jun-16 Physics 1 (Garcia) SJSU Money and Happiness Some people need a lot of money to make them happy. Some don’t. Some materials, such as water, need a lot of energy to raise their temperature. Some materials, such as iron, need little energy to raise their temperature. Nicole Richie & Paris Hilton MAHATMA GANDHI

4-Jun-16 Physics 1 (Garcia) SJSU Increasing Internal Energy Can increase internal energy (and temperature) by tapping energy sources. Chemical energy released in fire Electric energy heats burner

4-Jun-16 Physics 1 (Garcia) SJSU Work and Heat May increase internal energy by exerting a force to do mechanical work. Rub hands together for warmth Strike an iron surface with great force and red-hot sparks are created

4-Jun-16 Physics 1 (Garcia) SJSU Specific Heat Capacity Specific heat capacity is the internal energy required to raise one gram of a material by one degree of temperature. Filling has high specific heat capacity Crust has low specific heat capacity Filling and crust at same temperature yet mouth burned only by the filling.

4-Jun-16 Physics 1 (Garcia) SJSU Check Yourself Why does a piece of watermelon stay cool for a longer time than sandwiches do when both are removed from a cooler on a hot day? Why is it that the climate in the desert is so hot during the day yet so cold at night?

4-Jun-16 Physics 1 (Garcia) SJSU Demo: Boil Water in Paper Cup Because of high heat capacity of water, the large amount of heat added by the flame raises the temperature of the water until boiling. If the cup is filled with sand instead of water then it burns quickly. Cup with sand Cup with water

4-Jun-16 Physics 1 (Garcia) SJSU Thermal Expansion Due to increased molecular motion, most materials expand as temperature increases. Sidewalk buckles and cracks due to expansion on a hot summer day Space allows for expansion

Thermal Expansion Water is an exception. –Water contracts as it cools down to 4 degrees Celsius, then expands as it cools down to 0 degrees Celsius. This is how pot holes form, soda bottles explode when left in the freezer, and ice cubes float 4-Jun-16 Physics 1 (Garcia) SJSU

4-Jun-16 Physics 1 (Garcia) SJSU Demo: Expansion of a Ring Metal ball barely fits past the metal ring. Not surprising that heated ball won’t pass through cold ring. Will cold ball pass through heated (expanded) ring?

4-Jun-16 Physics 1 (Garcia) SJSU Demo: Bi-metallic Strip Different materials have different rates of expansion. STEEL Brass Brass expands more than steel when heated Thermostat Bi-metallic Spiral strip HOT COLD

Temperature Conversions To convert Celsius to Kelvin K=C To convert Celsius to Fahrenheit F= 4-Jun-16 Physics 1 (Garcia) SJSU